Botany

Botany is the Science Olympiad event about plant life in general: how plants are built, how they grow and move water and sugar, how the major groups differ, where they came from, and what they mean for ecosystems and for people. The 2027 rules make it a broad, general-botany event. Next to the core of anatomy and physiology, the topic list names the history of botany, plant genetics, paleobotany, global energy and nutrient cycles, crops and plant products, genetically modified organisms, and plant diseases, including nutrient deficiencies. Division C adds four more areas: horticulture and aquaculture, plant biochemistry, plants in medicine and environmental management, and the importance of plant diversity.

There are no subtopic guides for botany, so this page covers the whole event. Each section takes one area of the 2027 outline, explains the mechanism behind it, works the formulas, and shows how archived tournament questions test it.

Event format

The two divisions share identical logistics in 2027. Only the topic list differs (see the next section).

Calculators. Class II means a stand-alone scientific calculator that is neither programmable nor graphing (a TI-30X or Casio fx-260 type). A lower class is always allowed. Graphing calculators, programmable non-graphing calculators and phone or watch apps are not. The class definitions are in the General Rules on soinc.org.

The notes sheet. You get exactly one sheet of letter paper, and you may use both sides. Lamination or a sheet protector is fine for durability, but a second sheet (even inside the same protector) is not, and neither are labels or tabs stuck onto the page. With a topic list this wide, the sheet should hold the things you cannot reason out: dates, names, deficiency symptoms, the hormone table and formulas.

Specimens and equipment. The supervisor brings everything that is examined, so expect real or preserved plant material, slides and microscopes at stations. If a supervisor uses toxic or irritating plants, or specimens kept in liquid (algae and protists, for example), they must be in closed, unbreakable containers. Practice focusing a compound microscope and identifying tissues on prepared slides before the tournament. Total magnification = ocular lens (usually 10×) × objective (4×, 10× or 40×), so 10× × 40× = 400×. Start on the lowest objective with the coarse knob, then switch up and use only the fine knob; the image is upside down and reversed, and moving the slide left moves the image right. The field of view shrinks as magnification rises (a 4.0 mm field at 40× is 0.40 mm at 400×), so estimate a cell's size by dividing the field diameter by the number of cells that span it.

Eye protection. The event page sets no event-specific eye-protection requirement; the General Rules and policies on soinc.org still apply.

What the rules cover

The 2027 rules describe Botany in three layers: the structure and function of the plant body, the broad divisions between groups of plants, and a numbered list of additional topics. Division B has 11 numbered topics; Division C has the same 11 plus four more. The rules set no level restrictions (Regional, State and National cover the same list) and give no specimen list or topic weights.

The source references for this table are the 2027 Botany pages (B11 for Division B, C13 for Division C), section 3, items b through d.

The plant body

A flowering plant has two organ systems. The root system (roots) anchors the plant, absorbs water and minerals and often stores food; the shoot system (stems, leaves, buds, flowers, fruits and seeds) photosynthesizes and reproduces. Tests often ask for the "six basic parts of a plant": the three vegetative organs (roots, stems, leaves) and the three reproductive ones (flowers, fruits, seeds). Not every plant has all of them (bryophytes have no true roots, stems or leaves; ferns and conifers have no flowers or fruits; dodder has almost no leaves).

Cells

Plant cells are eukaryotic. They share the basics of animal cells (nucleus, mitochondria, plasma membrane, endoplasmic reticulum, Golgi, ribosomes, cytoskeleton) and add three features that explain most of plant structure: a cell wall, a large central vacuole and plastids. Of these, chloroplasts and a cellulose wall are the features found in neither animal nor fungal cells (fungi have walls of chitin). Plant cells usually lack centrioles (and centrosomes of the animal type) and typical lysosomes; the vacuole does the lysosome's digestive job.

Plant cells divide with a cell plate that grows outward from a phragmoplast (a scaffold of microtubules that steers Golgi vesicles full of wall material to the cell's equator) to become the new wall, instead of pinching in two as animal cells do. Chloroplast membranes record how a chloroplast was acquired: green algae and plants (primary endosymbiosis) have two, while algae that gained theirs by secondary endosymbiosis have three (euglenoids) or four (brown algae).

Osmosis is the diffusion of water across a selectively permeable membrane, from the side with fewer dissolved solutes (higher water potential) to the side with more (lower water potential). Diffusion is the net movement of any substance from higher to lower concentration and needs no energy; active transport moves ions or sugars against their gradient using ATP (often through a proton pump).

Water and the cell. When a cell takes in water, its vacuole swells against the rigid wall and creates turgor pressure. Turgor keeps herbaceous stems and leaves upright and drives the opening of stomata; a wilted plant has lost turgor. The outcome depends on the solution outside the cell:

Tissues

Ground tissue inside the ring of vascular tissue is the pith; ground tissue outside it is the cortex. Both are mostly parenchyma that stores water, sugar and starch. A simple tissue has one cell type (parenchyma, collenchyma, sclerenchyma); a complex tissue has several (xylem, phloem, epidermis).

Why should xylem be dead? Empty, lignified tubes have no cytoplasm in the way, so water flows freely, and their thick walls do not collapse under the tension that pulls water up. Phloem must stay alive because sugar loading and pressure-flow need working membranes. Water passes between conducting cells through bordered pits, thin pit membranes framed by an overarching rim of secondary wall; in conifers the pit membrane has a central thickened torus that seals the pit like a valve if a neighboring tracheid fills with air, limiting the spread of embolisms. Vascular bundles are collateral when phloem lies outside the xylem on the same radius; open bundles keep a strip of cambium between xylem and phloem (eudicots, gymnosperms) and closed bundles have none (monocots); stems are endarch (the protoxylem, the first narrow xylem cells to mature, lies toward the center, with later, wider metaxylem outside it) and roots are exarch (protoxylem toward the outside).

The epidermis is usually one cell layer thick, covered by a waxy cuticle made of cutin and waxes, which limits water loss and keeps out pathogens and UV light; the cuticle covers all aerial parts (leaves, stems, fruits) but not roots, which must absorb water. Epidermal specialties include guard cells, trichomes (hairs that deter insects physically or with toxic, sticky or bad-tasting secretions from glandular tips, reflect light, and trap a humid layer of air that cuts water loss), root hairs (extensions of single epidermal cells that multiply absorbing surface), bulliform cells (large cells that let grass leaves roll up in drought) and hydathodes (pores at leaf margins through which guttation water escapes). In woody stems the epidermis is replaced by periderm, whose loose patches, lenticels, admit air. Secretory structures include nectaries, resin ducts (conifers) and laticifers (the latex of milkweed, poppy and rubber trees). Single specialized cells scattered among ordinary ones are idioblasts: many hold crystals of calcium oxalate, either needle-shaped raphides (bundled in cells of Dieffenbachia, taro and grape, which burn the mouth when chewed) or star-shaped druses, while cystoliths of calcium carbonate grow in leaf cells of figs and rubber plants. Crystals deter herbivores and store excess calcium. Fresh, living plant tissue is mostly water, typically about 80 to 95% of fresh mass in leaves and herbaceous parts (less in wood and seeds), which is why yields and growth are often measured as dry mass.

Roots, stems and leaves

Roots

A taproot system has one dominant main root that grows deep, with smaller laterals: it reaches deep water and anchors well, suiting dry places and most dicots (carrot, dandelion, oak). A fibrous root system is a dense mat of many similar, thin roots near the surface: it holds topsoil against erosion and soaks up rain quickly, typical of monocots such as grasses. Adventitious roots grow from stems or leaves rather than from another root, which is what cuttings must produce to succeed.

Root layers. In cross-section a young root has, from outside in, the epidermis (with root hairs), the cortex (storage), the endodermis with its waterproof Casparian strip (a band of lignin, later backed by suberin layers, in the radial and end walls that blocks water from slipping between cells), the pericycle (dividing cells that produce lateral roots), and the central vascular cylinder (stele). In a eudicot root the xylem forms a central star or X with phloem between its arms and no pith; in a monocot root a ring of xylem and phloem strands surrounds a central pith. Pericycle is a frequent test answer.

Stems

A stem is recognized by nodes (where leaves and buds attach) and the internodes between them, with a terminal bud at the tip and an axillary (lateral) bud in the angle (axil) above each leaf. An axillary bud may grow into a vegetative branch or a flowering branch. On a twig in winter, rings of bud-scale scars mark each year's starting point, leaf scars (with dots of bundle scars) mark where leaves fell, and lenticels dot the bark. Underground organs with nodes, internodes and buds are stems, not roots: ginger and iris rhizomes, potato tubers.

In a eudicot stem the vascular bundles form a ring, with cortex outside and pith inside, and a woody eudicot adds a cambium that makes annual rings and bark. In a monocot stem the bundles are scattered through the ground tissue, with no clear cortex or pith and no vascular cambium. A plant with a taproot, growth rings and bark is a woody eudicot or a conifer (gymnosperms also make wood and bark).

Growth forms: trees have one main woody trunk; shrubs have several woody stems from the base; vines climb or trail with flexible stems; lianas are woody vines; creeping plants grow flat along the ground.

Sharp structures differ in origin: thorns are stems, spines are leaves or leaf parts (cactus spines, barberry), and prickles are outgrowths of the epidermis and cortex that snap off easily (the "thorns" of roses and blackberries).

Leaves

A typical leaf has a flat blade (lamina), a stalk (petiole) and often a pair of stipules at the petiole base; a leaf with no petiole is sessile. Grass leaves have a sheath that wraps the stem and a small ligule where blade meets sheath. The upper surface is adaxial and the lower abaxial.

• Simple vs. compound. A simple leaf has one blade (it may be lobed, as in maple or oak, but the lobes do not reach the midrib). A compound leaf divides into separate leaflets: pinnately compound (leaflets along a central rachis: ash, walnut, rose), palmately compound (leaflets from one point: horse chestnut, buckeye, clover), or bipinnately compound (leaflets themselves divided: mimosa, honey locust). To tell a leaflet from a leaf, look for a bud: there is an axillary bud at the base of a whole leaf, never at the base of a leaflet. Compound leaves may help in hot or windy places: small leaflets shed heat quickly and flutter rather than tear in wind, light passes between them to lower leaves, and some trees (black locust, walnut) shed leaflets or whole leaves in drought.
• Arrangement (phyllotaxy). Alternate (one leaf per node, spiraling up the stem), opposite (two per node), decussate (opposite pairs, each pair at right angles to the next, which keeps leaves from shading the ones below), and whorled (three or more per node). Spiral phyllotaxy often follows Fibonacci fractions of a turn between successive leaves (1/2, 1/3, 2/5, 3/8, 5/13…), approaching the "golden angle" of about 137.5°, which spaces leaves for minimal overlap.
• Venation. Parallel (most monocots), netted or reticulate, either pinnate (one midrib with side veins, as in elm) or palmate (several main veins from the base, as in maple), and dichotomous (forking in twos, as in Ginkgo and many ferns).
• Shape and margin words for identification: linear, lanceolate (lance-shaped), ovate (egg-shaped, widest below the middle), obovate (widest above), elliptic, cordate (heart-shaped), deltoid (triangular), orbicular (round), sagittate (arrowhead); margins entire (smooth), serrate (saw-toothed, teeth pointing forward), dentate (teeth pointing outward), crenate (rounded teeth), lobed and undulate (wavy).

More morphology terms: -foliate counts leaves (a trifoliate plant bears leaves in threes), while -foliolate counts leaflets (a trifoliolate leaf, like clover, has three leaflets), though many tests use "trifoliate" for both; peltate leaves have the petiole attached in the middle of the blade (nasturtium); perfoliate leaves surround the stem so it seems to pierce them; decurrent leaf bases run down the stem as wings; ptyxis (vernation) is how a leaf is folded or rolled in the bud, such as the coiled fiddlehead of a fern (circinate); in concaulescence an axillary branch or flower stalk is fused for some distance to the main stem, so it seems to arise above its leaf; in recaulescence a leaf or bract is fused to the axillary shoot it subtends, so the flower stalk seems to grow out of the middle of the bract (as in linden).

Leaf anatomy. Under the cuticle and upper epidermis lie the column-shaped palisade mesophyll cells (where most photosynthesis happens) and the loosely packed spongy mesophyll, whose large air spaces let CO₂ diffuse quickly to every cell and water vapor out to the stomata. Veins (vascular bundles) are wrapped in a bundle sheath. In most eudicots the stomata sit mainly on the lower surface, which is shaded, cooler and out of direct sun, so less water is lost per unit of CO₂ gained. Grasses and many other monocots with upright leaves have stomata on both surfaces. Floating leaves (water lily) have stomata only on the upper surface, the only side touching air. The leaf area index is the total one-sided leaf area divided by the ground area beneath it (8 m² of leaves over 2 m² of ground gives LAI = 4).

Many organs are modified for other jobs, and tests like to ask which organ a structure really is:

Spore-forming bodies

The 2027 outline names spore-forming bodies alongside flowers, so expect station questions that show a moss capsule, a fern frond or a cone. Every land plant makes spores by meiosis inside a sporangium; the groups differ in where the sporangia sit and how spores are released.

Homospory (one spore type) is the rule in mosses, most ferns and horsetails. Heterospory (small microspores that become male gametophytes and large megaspores that become female gametophytes) evolved in Selaginella, some aquatic ferns and all seed plants. It is the step that made seeds possible.

Flowers

Angiosperm flowers are built from four whorls of modified leaves on a receptacle at the tip of a flower stalk (pedicel):

1. Sepals, together the calyx: usually green; protect the flower bud before it opens.
2. Petals, together the corolla: usually colored and scented; attract pollinators. Calyx plus corolla is the perianth. When sepals and petals look alike (lilies, tulips) they are called tepals.
3. Stamens, together the androecium (male): each an anther, where pollen forms, on a stalk-like filament.
4. Carpels, together the gynoecium (female): each a stigma that receives pollen, a style, and an ovary holding ovules. A pistil is a single carpel or several carpels fused together; stigma, style and ovary make up the pistil.

Nectaries secrete nectar as a reward. In pollination, pollen moves from an anther to a stigma, never the other way.

A plant whose flowers are all perfect is neither monoecious nor dioecious in the strict sense, though some tests loosely call any plant bearing both sexes "monoecious". Fusion has its own vocabulary: connation is fusion of like parts (petals fused into a tube, as in morning glory; stamens fused by their filaments, as in mallows and legumes), and adnation is fusion of unlike parts (stamens fused to petals, as in the mint and nightshade families). A rare radially symmetrical flower on a normally zygomorphic plant (orchid, snapdragon) is called peloric.

Anther attachment to the filament is described as basifixed (attached at the anther's base, held rigid, as in many sedges and tulips), adnate (the filament runs along the back of the anther), dorsifixed (attached on the back) or versatile (attached at a single point near the middle so the anther swings freely, as in grasses and lilies; the swinging shakes pollen loose into wind or onto visiting insects). Corolla shapes have names too: campanulate (bell-shaped: bellflowers, bluebells), tubular (honeysuckle, many hummingbird flowers; foxglove's is a long, bell-mouthed tube), funnelform (morning glory, petunia), salverform (a narrow tube flaring flat: phlox), rotate (flat and wheel-like: tomato, potato), cruciform (four petals in a cross: mustards), papilionaceous (butterfly-like banner, wings and keel: peas), bilabiate (two-lipped: mints, snapdragons) and ligulate (strap-shaped: sunflower ray florets). Placentation is how ovules attach inside the ovary: marginal along one seam of a single carpel (legumes); axile on a central column where partitions meet (tomato, citrus, lily; Solanaceae, whose two carpels sit obliquely); parietal on the outer wall (mustards, violets, papaya); free-central on a free central column (pinks, primroses); basal at the bottom of a one-chambered ovary (sunflower family).

Floral formulas pack all this into one line: ⊕ or * = actinomorphic, ↑ or % = zygomorphic, ⚥ or ☿ = bisexual; K = calyx, C = corolla, P = tepals, A = androecium (stamens), G = gynoecium (carpels); numbers give counts, ∞ means many, parentheses mean the parts are fused, and a line under G means a superior ovary (a line over it, inferior). So % ☿ K(5) C(5) A4 G(2) (the mint family) reads: zygomorphic, bisexual, 5 fused sepals, 5 fused petals, 4 stamens and 2 fused carpels. Read any formula left to right the same way: a number in parentheses means those parts are fused, and A(2+2) would mean four stamens in two pairs. Family examples: mustards ⊕ ☿ K4 C4 A2+4 G(2); nightshades ⊕ ☿ K(5) C(5) A5 G(2); legumes % ☿ K(5) C5 A(9)+1 G1; lilies ⊕ ☿ P3+3 A3+3 G(3).

Inflorescences. A single flower on its stalk is solitary; a cluster of flowers on one stalk system is an inflorescence (its main stalk is the peduncle). In indeterminate (racemose) inflorescences the tip keeps growing and the lowest or outermost flowers open first; in determinate (cymose) inflorescences the tip ends in a flower that opens first.

Inflorescences can be compound: a compound umbel has umbels of umbels (carrot, dill), a compound spike has spikelets along the axis (wheat), and a thyrse has a main axis bearing small cymes (lilac, grape). A verticillaster is a false whorl formed by pairs of small cymes at each node, the typical arrangement of flowers in the mint family (Lamiaceae). A fascicle is a tight bundle of flowers (or leaves, as in pine needles) from one point. A monochasial cyme has one branch at each node: if the new branches always arise on the same side it coils into a helicoid cyme (bostryx); if they alternate sides it forms a zigzag scorpioid cyme (cincinnus), as in forget-me-not and heliotrope. A dichasium branches in two at each node. A sunflower "flower" is a head: the outer ray florets (each with one strap-shaped ligule formed from fused petals) surround hundreds of tubular disk florets, and each disk floret makes one fruit.

The ABC model of flower development. Three classes of homeotic genes (master control genes that decide which kind of organ forms in a given position), acting in overlapping zones, set the identity of the four whorls: A alone makes sepals, A + B makes petals, B + C makes stamens, and C alone makes carpels; A and C repress each other. A plant without B function makes sepals, sepals, carpels, carpels; without C, the A zone spreads and the flower repeats sepals and petals indefinitely (like the double flowers of many garden roses and camellias, which come from weakened rather than lost C function); without A, C spreads and the flower makes carpels, stamens, stamens, carpels. The genes were worked out in Arabidopsis and snapdragon. Arabidopsis thaliana (mustard family) is plant biology's model organism because it is small, has a very small genome, completes its life cycle in about six weeks, self-pollinates and makes thousands of seeds.

Inside the anther and the ovule. In each anther, diploid microsporocytes (microspore mother cells) undergo meiosis to make haploid microspores; each microspore divides once by mitosis to become a pollen grain with a large tube cell and a small generative cell. The generative cell divides to make two sperm, before or after pollination. The pollen wall's tough outer layer (exine) is made of sporopollenin, which is why pollen fossilizes so well.

An ovule hangs from a stalk (funiculus) and has one or two protective integuments with a small opening, the micropyle, at one end; the base opposite it is the chalaza, and the tissue inside is the nucellus (the megasporangium). One megasporocyte undergoes meiosis to give four megaspores; three degenerate, and the survivor divides by mitosis three times to make the embryo sac, the female gametophyte, with eight nuclei in seven cells: the egg and two synergids at the micropylar end, three antipodal cells at the chalazal end, and a large central cell with two polar nuclei.

Pollination and fertilization. A compatible pollen grain on the stigma germinates, and its pollen tube grows down through the style (by tip growth, loosening pectin as it goes) toward the ovule, guided by peptide attractants released by the synergids. It usually enters through the micropyle (porogamy), less often through the integuments (mesogamy) or the chalaza (chalazogamy). The tube bursts into a synergid and releases two sperm, and double fertilization, unique to angiosperms (gnetophytes such as Ephedra show a simpler version that makes no endosperm), follows: one sperm fuses with the egg to form the diploid zygote, and the other fuses with the two polar nuclei of the central cell to form the triploid (3n) endosperm, the food store. Afterward the zygote grows into the embryo, the integuments harden into the seed coat, the ovule becomes the seed, and the ovary ripens into the fruit.

Fruits and seeds

A fruit is a mature, ripened ovary (sometimes with other flower parts attached) that contains the seeds. Its wall, the pericarp, has three layers: exocarp (the skin), mesocarp (often the flesh) and endocarp (the inner layer, stony in a peach pit). Fruits protect seeds and disperse them, and some aid germination (seeds that pass through an animal's gut are scarified and dropped with fertilizer). Botanically, tomatoes, cucumbers, peppers, eggplants, green beans, squash and corn kernels are all fruits; "vegetable" is a cooking word, not a botanical one. Fruits are classified first by how many flowers and carpels form them:

• Simple fruit: from one ovary of one flower (a single carpel or several fused carpels).
• Aggregate fruit (also called an etaerio): from many separate carpels of one flower, each forming a small fruitlet on a shared receptacle (raspberry and blackberry are aggregates of drupelets; magnolia of follicles).
• Multiple fruit: from the ovaries of many flowers of an inflorescence fused together (pineapple, mulberry, fig, breadfruit, Osage orange).
• Accessory (false) fruit: much of the flesh comes from tissue other than the ovary (the apple and pear from the floral cup; the strawberry from the swollen receptacle, its true fruits being the little "seeds", which are achenes).

ReferenceFruit types· 16 rows

Simple fleshy fruits first, then simple dry fruits (dehiscent ones split open; indehiscent ones do not).

16 rows

Type	Definition	Examples
Berry	Whole pericarp fleshy, usually several seeds	Tomato, grape, blueberry, pepper, eggplant, banana, avocado (one seed)
Hesperidium	Berry with a leathery, oil-dotted rind and juice-filled sacs in segments	Orange, lemon, lime, grapefruit
Pepo	Berry with a hard rind, from an inferior ovary	Squash, pumpkin, cucumber, watermelon, cantaloupe
Drupe	Fleshy, with a single seed inside a hard, stony endocarp (pit)	Peach, cherry, plum, apricot, olive, mango; coconut (fibrous drupe); almond (we eat the seed)
Pome	Accessory fruit: fleshy floral cup around a papery core (the true ovary)	Apple, pear, quince
Legume	Dry pod from one carpel that splits along two seams	Pea, bean, peanut (which ripens underground and does not split)
Follicle	Dry fruit from one carpel that splits along one seam	Milkweed, columbine, magnolia (aggregate)
Capsule	Dry fruit from several fused carpels, opening by slits, pores or a lid	Poppy (pores), lily, cotton, iris, Brazil nut (seeds inside)
Silique	Two-valved capsule with a central partition; a short one is a silicle	Mustard family (cabbage, radish, Arabidopsis)
Achene	Small, dry, one seed attached to the thin pericarp at one point	Buttercup, strawberry's surface "seeds", buckwheat
Cypsela	Achene-like fruit from an inferior ovary, often with a pappus	Sunflower "seed", dandelion
Caryopsis (grain)	One seed whose seed coat is fused to the pericarp	Wheat, corn, rice, oats: the grass family
Nut	Hard, dry pericarp around usually one seed, from a compound ovary, often in a cup or husk	Acorn, hazelnut, chestnut
Samara	Winged, dry, indehiscent fruit	Ash, elm; maples make a double samara
Schizocarp	Splits into one-seeded parts	Carrot, parsley, dill; maple's paired samaras
Syconium	Multiple fruit: a hollow fleshy receptacle lined with tiny flowers, pollinated by fig wasps	Fig

A peach is therefore a simple, fleshy drupe; a raspberry is an aggregate of drupelets; a pineapple is a multiple fruit; an apple is an accessory pome. Many "nuts" in the kitchen are not botanical nuts: peanuts are legume seeds, almonds and pecans are drupe seeds or stones, and Brazil nuts are seeds from a capsule. Whether a fruit ends up fleshy or dry depends mainly on how its pericarp layers develop, in particular how much they lignify. Seedless fruits come from parthenocarpy (fruit set without fertilization, natural in bananas and navel oranges, or induced with auxin or gibberellin sprays) or from sterile triploids (bananas, seedless watermelons). In stenospermocarpy pollination and fertilization happen but the embryos abort early, leaving tiny seed traces (Thompson Seedless and most seedless table grapes). In some tropical fruits the part we eat is an aril, a fleshy outgrowth around the seed: lychee, longan, rambutan, mangosteen and ackee (and the red cup of a yew); the juicy pomegranate "seed" coat is a related fleshy seed coat (sarcotesta).

Seed structure. A seed has three parts: a seed coat (testa, from the integuments), an embryo, and stored food (endosperm or cotyledons). On the coat, the hilum is the scar where the seed was attached to its stalk (funiculus), and the micropyle is the tiny pore beside it where water first enters. The embryo has a radicle (embryonic root), hypocotyl, epicotyl with the plumule (first shoot and leaves) and cotyledons (seed leaves). Endosperm usually starts as a free-nuclear (coenocytic) tissue, its nuclei dividing without cell walls, before walls form; coconut water is liquid free-nuclear endosperm and the white coconut meat is the cellular endosperm. In beans and peas the cotyledons absorbed the endosperm as the seed matured, so they are fat food stores (an exalbuminous seed); in corn, wheat and castor bean the endosperm remains (an albuminous seed). A grass grain adds the scutellum (its single cotyledon, which absorbs food from the endosperm), the coleoptile (sheath over the shoot) and coleorhiza (sheath over the radicle), and an aleurone layer around the endosperm. Flour is ground endosperm; whole-wheat flour also includes the bran (pericarp, seed coat and aleurone) and germ (embryo).

Seed dispersal moves seeds away from the parent, where they would compete with it and with each other:

Growth and differentiation

Meristems and the root tip

Plants grow from meristems, tissues of undifferentiated, dividing cells, and they keep growing all their lives (indeterminate growth). That is why growth happens only at particular places: the tips of roots and shoots, and the cylinders of cambium in woody stems.

• Apical meristems at root and shoot tips make the plant longer: primary growth, which every plant has. The shoot apical meristem also lays down leaf primordia and axillary buds at regular positions.
• Lateral meristems make it thicker: secondary growth. The vascular cambium adds secondary xylem inward and secondary phloem outward; the cork cambium (phellogen) makes cork outward, building the protective periderm (outer bark). Primary and secondary growth run at the same time in a woody plant: the tips lengthen while older parts thicken.
• Intercalary meristems at the base of grass leaves and internodes let a lawn regrow after mowing.

Just behind the apical meristem, cells sort into three primary meristems that build the three tissue systems:

A root tip shows growth and differentiation in sequence. The root cap protects the tip as it pushes through soil, secretes slimy mucigel, and senses gravity, steering the root. Behind the cap lies the zone of cell division (the meristem), then the zone of elongation (cells lengthen many times over and push the tip forward; this is where the root actually grows longer), then the zone of maturation (cells differentiate into xylem, phloem and epidermis, and root hairs appear). Lateral roots start deep inside, in the pericycle, and push out through the cortex. In roots that undergo secondary growth, the pericycle also forms the first cork cambium and part of the vascular cambium; most stems have no distinct pericycle (the term is used there only loosely for the outer edge of the vascular cylinder). Differentiation is the process by which genetically identical cells take on different structures and jobs. Many mature plant cells keep the ability to dedifferentiate and regenerate a whole plant (totipotency), which is what makes cuttings and tissue culture work. A tree grows upward only at its tips, so a nail driven into a trunk 5 feet up stays 5 feet up for as long as the tree lives.

The embryo in a seed already has the plant's axis: the radicle (embryonic root, the first organ to emerge at germination), the hypocotyl (stem below the cotyledons), the epicotyl (stem above the cotyledons) tipped by the plumule (the first shoot and leaves), and one or two cotyledons. Grasses add sheaths over both ends: the coleoptile over the shoot and the coleorhiza over the radicle.

Plant hormones

Hormones coordinate growth and differentiation. They act at very low concentrations, often far from where they are made, and usually in balance with one another, so the ratio between two hormones often matters more than either amount.

Auxin in detail. Auxin moves from cell to cell in one direction, from shoot tips toward the base (polar transport), because auxin efflux carriers (PIN proteins) sit on the lower side of each cell; it also travels long distances in the phloem. It makes cells elongate by the acid-growth mechanism: auxin activates plasma-membrane proton pumps (H⁺-ATPases), the wall acidifies, wall-loosening proteins (expansins) become active, and turgor stretches the loosened wall. The pumps use ATP, so a cell starved of oxygen (and therefore of respiratory ATP) cannot respond. At the gene level, auxin binds its receptor (TIR1), which tags Aux/IAA repressor proteins for destruction; with the repressors gone, ARF transcription factors switch on auxin-response genes. Auxin also patterns the plant: leaf arrangement (phyllotaxy), vein and vascular differentiation, root initiation and fruit development. Spraying tomato flowers with an auxin "blossom set" product makes fruit set without pollination (parthenocarpy).

Apical dominance is the shoot tip's suppression of the axillary buds below it. Auxin flowing down from the tip (with strigolactones) keeps the buds dormant; cytokinin from the roots promotes their growth. Remove the tip (pruning, pinching or grazing) and the auxin supply drops, so side buds grow and the plant bushes out.

Gibberellin in detail. Gibberellins were discovered in Japan through the "foolish seedling" (bakanae) disease of rice, in which the fungus Gibberella fujikuroi secretes GA and infected seedlings grow absurdly tall and fall over. In a germinating cereal grain, the embryo releases GA, which diffuses to the aleurone layer (the protein-rich outer layer of the endosperm) and induces the enzyme α-amylase; the enzyme digests endosperm starch to sugars that feed the seedling. Brewers exploit this in malting.

Ethylene in detail. Climacteric fruits (banana, apple, pear, tomato, avocado, peach) ripen after picking with a burst of respiration and ethylene; each ripening fruit makes ethylene that speeds ripening in itself and its neighbors (positive feedback). Non-climacteric fruits (citrus, grapes, strawberries, cherries) have no ethylene burst and do not get sweeter after harvest. A seedling that meets an obstacle such as a stone makes ethylene and shows the triple response: its stem slows elongation, thickens and grows sideways, letting it get around the obstacle. Autumn senescence is triggered mainly by shortening days (longer nights) and falling temperatures. Chlorophyll is broken down and its nitrogen and magnesium are moved back into the stem, unmasking the yellow and orange carotenoids that were there all along; many trees also make new red anthocyanins in the fall, most brightly after sunny days and cool (not freezing) nights. In autumn, falling auxin from an aging leaf and rising ethylene trigger enzymes in the abscission zone at the base of the petiole that dissolve the cell walls of a separation layer, while a protective layer of corky cells seals the scar.

Tropisms and other movements

A tropism is directional growth toward (positive) or away from (negative) a stimulus. It is growth, so it is slow and permanent.

Gravitropism and the statolith hypothesis. Gravity is sensed by statoliths, dense starch-filled amyloplasts, in gravity-sensing cells (statocytes): the columella cells of the root cap and in the endodermis of shoots. When a root is tipped sideways, the statoliths settle to the new lower side of the cells; the PIN3 auxin carriers move to that lower side, so auxin flows to the lower flank of the root. In roots, high auxin inhibits elongation, so the lower side grows less and the root curves down. In shoots, auxin promotes elongation, so the lower side grows more and the shoot curves up. In shoots the statocytes are in the endodermis (the innermost layer of the cortex, the "starch sheath"); in grass seedlings the coleoptile tip is needed for the full bending response, as it is for phototropism.

Auxin's discovery is a classic experiment sequence. Charles and Francis Darwin (1880) showed that a grass coleoptile bends toward light only if its tip is uncovered, so the tip senses light and sends a signal down. Peter Boysen-Jensen (1913) showed the signal passes through gelatin but not through mica, so it is a chemical. Árpád Paál (1919) placed a cut tip off-center on the stump in darkness and got bending away from that side. Frits Went (1926) collected the chemical in agar blocks, which alone made decapitated coleoptiles bend; the name auxin was coined a few years later (Kögl and Haagen-Smit, 1931).

A nastic movement is a response whose direction does not depend on where the stimulus comes from; most are fast, reversible turgor changes in a hinge-like pulvinus at the leaf base. Nyctinasty is the nightly folding of leaves in many legumes ("sleep movements"); thigmonasty (seismonasty) is the folding of sensitive-plant (Mimosa pudica) leaflets when touched and the snapping of a Venus flytrap. Thigmomorphogenesis is a slower, lasting response to repeated touch or wind: plants that are rubbed, shaken or wind-blown grow shorter and stockier (ethylene is involved), which is why outdoor-hardened seedlings are sturdier than greenhouse ones. Heliotropism (solar tracking) is the daily turning of leaves or flowers to follow the sun, driven by pulvini in many legumes and by stem growth in young sunflowers (mature sunflower heads stop tracking and face east). A taxis is different again: movement of a whole motile organism or cell toward or away from a stimulus, such as phototaxis of swimming Chlamydomonas or chemotaxis of fern and moss sperm toward archegonia.

Light, day length and timing

Plants read light through photoreceptors. Phytochrome exists in two forms that convert into each other: Pr absorbs red light (about 660 nm) and becomes Pfr, the active form; Pfr absorbs far-red light (about 730 nm) and reverts to Pr (it also drifts back slowly in darkness). Sunlight has more red than far-red, so daytime leaves are rich in Pfr. Phytochrome controls seed germination in light-requiring seeds such as lettuce (red promotes, far-red cancels, and the last flash wins), de-etiolation of seedlings reaching light, shade avoidance (canopy shade is rich in far-red, so plants stretch), and flowering time. Cryptochromes and phototropins absorb blue light and control phototropism, stomatal opening, de-etiolation and the circadian clock. A seedling in the dark is etiolated: long, pale and spindly, with tiny leaves and a hooked tip (the apical hook, formed by the hypocotyl in beans and by the epicotyl in peas, protects the shoot tip while it pushes through soil). A succulent kept in dim light stretches the same way; brighter light, especially blue and red, keeps it compact.

Photoperiodism is the flowering response to day length, which plants actually measure as the length of the uninterrupted night.

A far-red flash right after the red flash cancels the red flash's effect. So a short-day plant needing at least 14 hours of darkness, given a 16-hour night interrupted by red then far-red light, still flowers; given 13 hours of darkness, or a night broken by a final red flash, it does not.

Vernalization is the induction of flowering by a long cold period: winter wheat and many biennials (carrots, cabbage, foxglove) will not flower without a winter. Chilling hours do the same for the dormant buds of many fruit trees. The circadian clock runs on a roughly 24-hour cycle, timing stomatal opening and leaf movements and letting the plant compare night length with an internal standard. Photoperiodic responses vary: some plants flower after a single inductive night (cocklebur), others need many; young plants are often unresponsive until they reach a minimum age (juvenility); temperature modifies the response; and populations from higher latitudes have different critical night lengths than those from lower latitudes. FT protein (florigen) also influences tuber formation and bud dormancy.

Germination and dormancy

Germination is the resumption of growth by a seed embryo, ending when the radicle emerges. It starts with imbibition, the rapid uptake of water by the dry seed, which activates enzymes and respiration; GA then mobilizes stored food (via α-amylase in cereals). Seeds need water, oxygen and a suitable temperature; some also need light (lettuce) or darkness, while many germinate without light at all. In epigeal germination the hypocotyl lifts the cotyledons above ground (beans, sunflowers); in hypogeal germination the cotyledons stay below ground (peas, corn, oaks).

Dormancy keeps a viable seed from germinating even when conditions seem right, so it waits for a season when the seedling can survive. Dormancy has several causes, each with a matching treatment:

A seed that is not dormant but simply lacks water, oxygen or warmth is quiescent: it germinates as soon as conditions allow. True dormancy blocks germination even under good conditions until a specific cue (cold, light, a broken coat, leaching) is met. Buds go dormant too: shortening days and ABA trigger winter dormancy in temperate trees, and chilling hours later release it.

Woody and herbaceous growth

Woody plants keep a vascular cambium and cork cambium active for years, so they lay down wood and bark and grow thicker each season. Each year's wood forms an annual ring: wide, thin-walled earlywood (springwood) cells formed when water is plentiful, and narrow, thick-walled latewood (summerwood) cells formed later in the season. The visible ring is the sharp boundary where small latewood cells meet the next spring's large earlywood cells. Wide rings record good growing years; narrow rings record drought or cold, which is the basis of dendrochronology (tree-ring dating). Tropical trees with no cold or dry season may show no clear rings.

In a trunk cross-section, from the center out: pith (in young stems), heartwood (older, inner, nonconducting wood, often darker because it fills with resins, tannins and other extractives; vessels may be plugged by tyloses, balloon-like outgrowths of neighboring cells that also wall off infections), sapwood (younger, outer wood that still conducts water), the vascular cambium (the thin layer that divides wood from bark), secondary phloem (inner bark, carrying sugar), the cork cambium and cork (outer bark). Everything outside the vascular cambium is bark, so stripping a ring of bark (girdling) cuts the phloem and starves the roots, killing the tree. Girdling a single branch traps the sugar made by its leaves above the cut, so fruits on that branch grow larger and sweeter; growers use a thin girdle on grapevines and some fruit trees for exactly this effect, and the wound heals over before the roots suffer. Wood is mostly cellulose (about 40 to 50% of dry mass), hemicellulose (roughly 20 to 30%) and lignin (roughly 20 to 30%, usually higher in softwoods than hardwoods). Reaction wood forms in leaning stems and branches: conifers make compression wood on the lower side, pushing the stem up; angiosperm trees make tension wood on the upper side, pulling it up. In an older tree, secondary xylem (wood) is by far the thickest layer; the living phloem and bark form a thin outer skin, because the cambium adds much more xylem than phloem each year and old phloem is crushed and shed.

Herbaceous plants have little or no secondary growth; their stems are soft and green and often die back each year. Lifespan categories (annual, biennial, perennial) cut across this (see Woody vs. herbaceous and life spans). Monocot "trees" such as palms thicken without a true vascular cambium, so they lack annual rings.

Transport and storage

Two separate pipelines run through a vascular plant. Xylem carries water and dissolved minerals one way, up from roots to leaves, driven by transpiration (cohesion-tension). Phloem carries sugars and other organic molecules (amino acids, hormones such as auxin, some viruses) in either direction from sources to sinks, driven by pressure flow. Xylem is dead at maturity; phloem must be alive.

Water and minerals

Water potential (Ψ) measures water's tendency to move, in units of pressure: pure water at atmospheric pressure is 0, and dissolved solutes or tension make it negative. Water always moves from higher (less negative) to lower (more negative) Ψ, and the steepest drop is from the leaf to the air. The pathway runs soil → root hair → cortex → endodermis → xylem → leaf → stomata → air. In the cortex, water travels through cell walls and the spaces between cells (the apoplastic route), through cytoplasm linked by plasmodesmata (the symplastic route), and by crossing membranes from cell to cell (the transmembrane or transcellular route). At the endodermis the Casparian strip blocks the wall route, so everything entering the xylem must cross a living membrane, letting the root choose which ions enter and stopping water and solutes from leaking back out. Root cells actively pump in mineral ions, which lowers the root's water potential so water follows by osmosis; that is how water enters a root but does not leave it.

A cell placed in a solution comes to equilibrium when its Ψ equals the solution's. In a classic lab, potato cores are soaked in a sucrose series; the concentration at which their mass does not change has the same Ψ as the potato tissue.

Cohesion-tension. Water evaporating from the leaf (transpiration) pulls the xylem column upward under tension. Water molecules cohere to each other through hydrogen bonds and adhere to the hydrophilic xylem walls, so the column moves as one unbroken thread from leaf to root. An air bubble (cavitation or embolism) breaks the column. At night, when transpiration stops, roots that keep pumping ions can push water up a short way by root pressure, which forces droplets out of hydathodes at the leaf margins (guttation). The transpiration stream also carries minerals up and cools the leaf as water evaporates.

Transpiration loses enormous amounts of water: the large majority of the water a plant takes up (well over 90%) leaves through the stomata as vapor. It is the unavoidable cost of opening stomata to take in CO₂, but it also cools leaves and moves minerals upward. Rate factors:

Designing a plant experiment. Tests often ask you to design or critique one (for example, the effect of a hormone, fertilizer or light color on growth). Change one independent variable across a series of treatment levels (a concentration series such as 0, 1, 10 and 100 mg/L, where 0 is the control); keep everything else constant (species and age of plants, pot size, soil, water, light, temperature); measure a dependent variable that reflects growth (height, leaf number or area, fresh or better dry mass, root length, germination percentage); use replicates (several plants per treatment, randomly placed) so one odd plant does not decide the result; and report means with variation. Any accident that affects one group (a pot knocked over, roots disturbed) adds an uncontrolled variable, so that plant's trial should be restarted or excluded. A transpiration experiment is a standard design question: the independent variable is the factor you change (humidity, light, wind from a fan), the dependent variable is water loss per time per leaf area, and controls keep everything else equal (species, leaf area, temperature, soil water). Expect the highest rate at low humidity, bright light, warm temperature and strong wind.

Minerals reach the root by diffusion and mass flow in soil water, and mycorrhizal fungi, which associate with about 80 to 90% of land plants, extend the absorbing surface far beyond the root, improving phosphorus and water uptake in exchange for sugar. Evapotranspiration is the total water returned to the air from a landscape: evaporation from soil and water surfaces plus transpiration from plants.

Gases

Leaves exchange CO₂ and O₂ through stomata (singular stoma, also stomate). Each stoma is a pore between two guard cells, often flanked by subsidiary cells. When guard cells actively take in potassium ions (K⁺, with chloride and malate), their water potential falls, water enters, turgor rises, and because their inner walls are thicker and their cellulose microfibrils run radially, the swelling cells bow apart and open the pore. Losing K⁺ reverses this. Blue light (sensed by phototropins) and low internal CO₂ open stomata; ABA, high internal CO₂, darkness, water stress and very high temperatures close them.

Stems with bark breathe through lenticels, loose patches in the periderm. Roots and every living cell need O₂ for respiration, which is why waterlogged soil kills many plants. Wetland plants cope with aerenchyma, tissue with large air channels that carry O₂ down to submerged roots, and mangroves with pneumatophores. Gas moves inside the leaf by diffusion through the air spaces of the spongy mesophyll.

Sugars and storage

Sugar (mostly sucrose) moves in the phloem from a source (a mature, photosynthesizing leaf, or a storage organ being emptied) to a sink (roots, fruits, seeds, growing tips, young leaves, storage organs being filled). The pressure-flow (mass-flow) model, proposed by Ernst Münch in 1930, explains it: companion cells load sucrose into sieve tubes at the source (often actively, using a proton gradient); the high sugar concentration draws water in from the neighboring xylem by osmosis and raises the pressure; at the sink, sugar is unloaded and water leaves, lowering the pressure; sap flows from high to low pressure through the sieve plates. Phloem can run in either direction depending on where sources and sinks are; xylem runs only upward. Aphids, whose mouthparts tap single sieve tubes, were used to sample phloem sap and prove the pressure. Loading follows one of three routes: apoplastic loading, in which sucrose leaves mesophyll cells into the cell walls and is pumped into companion cells by H⁺-sucrose symporters (many crops); symplastic loading through plasmodesmata; and polymer trapping, in which sucrose diffusing into specialized intermediary cells is built into larger sugars (raffinose and stachyose) too big to diffuse back.

Plants store energy mainly as starch (in amyloplasts of roots, tubers, seeds and stem pith), as sugars in vacuoles (sugarcane, sugar beets), and as oils in seeds (sunflower, canola). The same storage organ can be a sink in one season and a source in the next: a potato tuber fills in summer and feeds the new shoots the following spring.

Major groups of plants

The 2027 rules name four contrasts (algae vs. land plants, monocots vs. dicots, embryophytes vs. cryptogams, woody vs. herbaceous) and ask for the differences between the major taxonomic groups. The section starts with the algae vs. land plants and embryophyte vs. cryptogam contrasts, then gives an overview table and the life-cycle figure, and then a subsection for each group with the details tests ask.

Algae vs. multicellular land plants

"Algae" is an informal word for photosynthetic organisms that are not land plants. It covers single cells (Chlamydomonas, diatoms), colonies (Volvox) and large multicellular seaweeds (kelp), and it spans several unrelated lineages. Only the green algae are close relatives of plants; red algae are more distant, and brown algae, diatoms and golden algae belong to a different lineage altogether (the stramenopiles, which got their chloroplasts by secondary endosymbiosis). "Blue-green algae" are cyanobacteria, which are bacteria. Tests tell algal groups apart by pigments and storage products:

Algal bodies come in five plans: unicellular (Chlamydomonas, Euglena, diatoms), colonial (Volvox, a hollow ball of hundreds to thousands of cells with some division of labor, usually treated as the threshold of multicellularity), filamentous (Spirogyra, an unbranched chain of cells with spiral chloroplasts), sheet-like or bladed (Ulva, sea lettuce, two cells thick; kelps) and coenocytic (below). Green algae show every type of gamete pairing: isogamy (two gametes of the same size and shape, both swimming, as in many Chlamydomonas), anisogamy (two swimming gametes of different sizes) and oogamy (a large, non-motile egg and a small, swimming or carried sperm, as in Volvox, Oedogonium, Chara and all land plants). A coenocyte is a multinucleate cell: many nuclei share one cytoplasm without walls between them, as in Vaucheria, the green alga Caulerpa and many water molds.

Land plants evolved from freshwater charophyte green algae more than 470 million years ago. Charophytes and land plants share chlorophylls a and b, starch storage and cellulose walls (with all green algae), plus traits found only in this pair: rosette-shaped cellulose-synthesizing complexes in the plasma membrane, a phragmoplast that builds the new cell wall during cell division, sporopollenin, a tough polymer that coats charophyte zygotes and plant spores and keeps them from drying out, peroxisome enzymes that help handle photorespiration, and similar flagellated sperm.

The bolded traits in the land-plant column (alternation of generations with dependent embryos, walled spores in sporangia, multicellular gametangia, apical meristems) are the derived traits that define land plants. Life on land offered more light (unfiltered by water), freely available CO₂, minerals from weathered rock, and at first few herbivores or pathogens. It also demanded new solutions to drying out (cuticle, stomata, sporopollenin), support (lignin), moving water (vascular tissue), getting sperm to egg without swimming (pollen) and protecting the embryo (seeds). Mycorrhizal fungi, present in the earliest land-plant fossils, helped the first plants take up water and minerals before true roots existed.

Embryophytes vs. cryptogams

These are two older terms that overlap, which makes them easy to confuse. Embryophytes are the land plants: every group whose embryo develops inside the parent (mosses, liverworts, hornworts, ferns and their allies, gymnosperms and angiosperms). Being an embryophyte is what makes something a "true plant" (kingdom Plantae in the narrow sense). Cryptogams ("hidden reproduction") is a traditional name for organisms that reproduce by spores and have no flowers or seeds: algae, bryophytes and ferns (older texts also included fungi and lichens). The opposite term is phanerogams, the seed plants. So a fern is both an embryophyte and a cryptogam, a green alga is a cryptogam but not an embryophyte, and a pine is an embryophyte but not a cryptogam. Keeping the zygote and young embryo inside the archegonium protects it from drying and UV light and lets the parent feed it, a key advantage on land.

The major taxonomic groups

Every land plant alternates between a haploid gametophyte (n, makes gametes by mitosis) and a diploid sporophyte (2n, makes spores by meiosis). One diploid spore mother cell (sporocyte) in a sporangium undergoes meiosis to give four haploid spores; each spore grows into a gametophyte; gametes fuse into a diploid zygote; the zygote grows into the next sporophyte. Spores, pollen, eggs, sperm and gametophytes are haploid; zygotes, embryos and sporophytes are diploid. The trend across the table is a shrinking gametophyte: large and free-living in mosses, small but independent in ferns, microscopic and dependent on the sporophyte in seed plants. Other evolutionary trends run the same direction: from homospory to heterospory, from swimming sperm to pollen, from spores to seeds, and from no vascular tissue to tracheids and then vessels.

Mitosis copies a cell into two genetically identical cells with the same chromosome number (growth, repair, asexual reproduction, and making gametes from a haploid gametophyte); meiosis halves the chromosome number and shuffles alleles, giving four genetically different haploid cells. In animals meiosis makes gametes; in plants it makes spores.

Order of appearance in the fossil record (oldest first): bryophyte-grade plants (liverworts are often placed first) → lycophytes → ferns and horsetails → seed ferns and gymnosperms → angiosperms. All vascular plants and some extinct relatives form the polysporangiophytes, plants whose sporophytes branch and bear many sporangia; bryophytes, with a single unbranched sporophyte and one capsule, are outside this group. Plants with vascular tissue are tracheophytes (vascular plants), which include the lycophytes, ferns and horsetails (together sometimes called pteridophytes), gymnosperms and angiosperms.

Bryophytes: liverworts, mosses and hornworts

Bryophytes are small, nonvascular land plants of damp places. The green, leafy or ribbon-like plant you see is the gametophyte; it is anchored by rhizoids (not true roots) and absorbs water and minerals directly over its whole surface, like an alga. With no lignified xylem, bryophytes stay short. Sperm swim from the antheridium through a film of water to the egg in the flask-shaped archegonium; the zygote grows into a small, unbranched sporophyte that stays attached to the gametophyte and depends on it for food. A spore germinates into a threadlike protonema (in mosses), which buds into leafy gametophytes. Mosses and liverworts are pioneer species on bare rock and soil.

Bryophytes lack lignified xylem, but many mosses have simple conducting cells in the center of the stem, hydroids (water) and leptoids (sugar); a few liverworts have comparable water-conducting cells, while hornworts have none. Mucilage is common: liverworts have mucilage cells and slime papillae, and hornworts have mucilage-filled cavities in the thallus that house their Nostoc colonies. Functions of the moss sporophyte parts are a classic short-answer item: the foot anchors the sporophyte in the gametophyte and absorbs water and nutrients from it; the seta lifts the capsule into moving air for better spore dispersal and conducts water and nutrients from the foot up to the developing capsule; the capsule (sporangium) makes spores by meiosis; the peristome teeth open and close with humidity to meter spores out. Many mosses separate or time their antheridia and archegonia to avoid self-fertilization, which would give offspring with no new genetic variation.

Seedless vascular plants: lycophytes, ferns and horsetails

Vascular tissue (xylem stiffened with lignin, plus phloem) lets these plants grow tall, and in them the sporophyte became the dominant, independent generation. They still need water for swimming sperm, and their gametophytes are small but free-living.

The fern life cycle. The fern plant with fronds is the diploid sporophyte. Sporangia, clustered into sori on the underside of fertile fronds (often covered by an indusium), make haploid spores by meiosis; the annulus flings them out. A spore grows into a small, heart-shaped, photosynthetic gametophyte, the prothallus, which bears antheridia and archegonia on its underside and is independent of the sporophyte. Fern gametophytes often make antheridia before archegonia (protandry), which favors outcrossing. Sperm swim to the egg; the zygote grows into a new sporophyte that soon outgrows and replaces the prothallus. Some ferns show frond dimorphism, with separate fertile (spore-bearing) and sterile (photosynthetic) fronds, as in sensitive fern and cinnamon fern. The water fern Azolla houses nitrogen-fixing cyanobacteria (Anabaena) and has long been used as a green manure in rice paddies.

Gymnosperms

Gymnosperms ("naked seeds") bear seeds exposed on the surface of cone scales or similar structures, not enclosed in an ovary, so they make no flowers and no fruits. They are heterosporous seed plants with a dominant sporophyte, a seed coat around each seed, and pollen (the immature male gametophyte) that wind carries to the ovule, so no water is needed for fertilization (cycads and ginkgo still release swimming sperm inside the ovule). Their xylem is almost all tracheids; most lack vessels. Their wood is called softwood, whereas angiosperm trees give hardwood (with vessels and fibers), though some "softwoods" are harder than some "hardwoods".

The pine life cycle. The tree is the sporophyte. Small pollen cones (microsporangiate) grow in clusters, typically on the lower branches, and make enormous amounts of winged pollen grains (immature male gametophytes) by meiosis and mitosis. Larger seed cones (ovulate), typically on the upper branches, carry two ovules on each scale. At pollination, a sticky pollination drop oozing from the micropyle catches pollen and draws it into the ovule. Fertilization comes about 15 months later, after the pollen tube has slowly grown through the megasporangium; the seeds then mature (usually in the autumn of the second year) and are shed from the opened cone. Each seed holds a diploid embryo, a haploid food supply (the female gametophyte tissue, not endosperm) and a seed coat. Gymnosperms dominated from the Permian through the Jurassic; conifers first appeared in the Late Carboniferous, related to the extinct Cordaites.

Angiosperms

Angiosperms (phylum Anthophyta, also Magnoliophyta) are the flowering plants, with roughly 350,000 described species (estimates run from about 300,000 to 370,000), close to 90% of all land plant species. What sets them apart:

• Flowers, which recruit animal pollinators (co-evolution with insects, birds and bats) and speed up pollination.
• Ovules enclosed in a carpel, so the seeds develop inside an ovary that ripens into a fruit, which protects seeds and aids their dispersal.
• Double fertilization, which makes a triploid endosperm only after fertilization succeeds, so the plant does not waste food on unfertilized ovules.
• Highly reduced gametophytes: the male gametophyte is the pollen grain (a tube cell plus a generative cell that divides into two sperm), and the female gametophyte is the embryo sac (typically seven cells with eight nuclei).
• Vessel elements in the xylem and companion cells in the phloem.
• A short generation time in many species, allowing herbaceous annual life cycles.

Modern classification (APG) splits angiosperms into a few early branches, the ANA grade (Amborella, water lilies, star anise), and the mesangiosperms: magnoliids (magnolias, laurels, avocado, black pepper), Chloranthales, monocots, Ceratophyllum (coontail) and eudicots. Angiosperms appear in the fossil record in the Early Cretaceous, about 130 million years ago, and dominated most land ecosystems by the end of the Cretaceous.

Plant and algal groups at a glance

Algae and plants are told apart on tests by the same few traits: which pigments they have, how many membranes wrap the chloroplast (two for primary plastids, three or four for secondary ones), what food they store and what the wall is made of, and their body plan and life cycle. This table covers every lineage tests ask about, from cyanobacteria and minor algal groups to extinct seed plants, so you can compare any two rows directly; "primary" plastids came from an engulfed cyanobacterium and "secondary" plastids from an engulfed red or green alga. All land plants share chlorophylls a and b, two-membrane chloroplasts, starch and cellulose walls, so their rows focus on body and life cycle.

ReferencePlant and algal groups· 52 rows

Chl = chlorophyll. Membranes = number of membranes around the plastid. Gametophyte = haploid (n); sporophyte = diploid (2n). † = extinct.

52 rows

Group	Rank or clade	Pigments / chloroplast membranes	Storage product and wall	Body and life cycle	Examples and notes
Cyanobacteria ("blue-green algae")	Domain Bacteria; phylum Cyanobacteria	Chl a, phycobilins (phycocyanin, phycoerythrin) in phycobilisomes; no chloroplast (thylakoids free in cytoplasm)	Cyanophycean (glycogen-like) starch; peptidoglycan wall, often a mucilage sheath	Unicells, colonies, filaments; heterocysts fix N₂, akinetes survive stress; asexual only	Nostoc, Anabaena, Oscillatoria, Spirulina, Microcystis (toxic blooms); stromatolites; made Earth's oxygen; ancestors of all plastids
Glaucophytes	Phylum Glaucophyta; Archaeplastida	Chl a, phycobilins; 2 membranes with a peptidoglycan layer between them (cyanelle or muroplast)	Starch in cytoplasm	Small freshwater unicells; no sex known	Cyanophora, Glaucocystis; plastid most like a free cyanobacterium
Red algae	Phylum Rhodophyta; Archaeplastida	Chl a, phycoerythrin, phycocyanin; 2 membranes; unstacked thylakoids	Floridean starch in cytoplasm; cellulose with agar and carrageenan; coralline algae add CaCO₃	Mostly marine seaweeds; no flagella or centrioles at any stage; often a three-phase life cycle (gametophyte, carposporophyte, tetrasporophyte)	Nori (Pyropia, Porphyra), Gelidium, Gracilaria, Irish moss (Chondrus), Corallina; grow deepest of seaweeds
Chlorophyceae	Class in phylum Chlorophyta (green algae)	Chl a and b, carotenoids; 2 membranes	Starch inside chloroplast, often around pyrenoids; cellulose or glycoprotein wall	Flagellated unicells, colonies, filaments; mostly haplontic (zygotic meiosis)	Chlamydomonas (isogamy, eyespot), Volvox (oogamy), Oedogonium; mostly freshwater
Ulvophyceae	Class in Chlorophyta	Chl a and b; 2 membranes	Starch; cellulose or other polysaccharide walls	Sheets, filaments, giant single or coenocytic cells; Ulva alternates isomorphic generations	Sea lettuce (Ulva), Acetabularia (one giant cell; Hämmerling's nucleus experiments), Caulerpa (invasive "killer alga"), Codium, Cladophora
Trebouxiophyceae	Class in Chlorophyta	Chl a and b; 2 membranes	Starch; cellulose	Mostly non-flagellate unicells; asexual autospores	Chlorella (studied by Calvin), Trebouxia (the commonest lichen partner)
Prasinophytes	Early-diverging Chlorophyta (a grade)	Chl a and b; 2 membranes	Starch; organic body scales or none	Tiny scaly flagellates and picoplankton	Ostreococcus (smallest known free-living eukaryote), Micromonas
Early charophytes	Streptophyta (with land plants): Mesostigmatophyceae, Chlorokybophyceae, Klebsormidiophyceae	Chl a and b; 2 membranes	Starch; cellulose	Unicells, packets, unbranched filaments	Mesostigma, Klebsormidium (filaments on soil and bark)
Stoneworts (Charales)	Class Charophyceae, Streptophyta	Chl a and b; 2 membranes	Starch; cellulose, often crusted with CaCO₃ in Chara	Large whorled nodes and giant multinucleate internode cells; oogonium wrapped in spiral cells; haplontic; phragmoplast	Chara, Nitella; cytoplasmic streaming studies; once considered closest to land plants
Coleochaetales	Class Coleochaetophyceae, Streptophyta	Chl a and b; 2 membranes	Starch; cellulose	Disk-shaped, parenchyma-like or branched; sheathed hairs; zygote retained on parent and covered by cells; oogamous; phragmoplast	Coleochaete; hints of the retained, nourished zygote of land plants
Conjugating algae (Zygnematales and desmids)	Class Zygnematophyceae, Streptophyta	Chl a and b; 2 membranes; ribbon (Spirogyra) or star (Zygnema) chloroplasts	Starch; cellulose	No flagellated cells; sex by conjugation (scalariform or lateral); haplontic	Spirogyra, Zygnema, desmids (Closterium, Micrasterias); now judged the sister group of land plants
Euglenoids	Euglenozoa (Discoba); secondary green plastid	Chl a and b; 3 membranes	Paramylon (β-1,3-glucan) in cytoplasm; no wall, a protein pellicle	Flagellated unicells with eyespot; longitudinal fission; no sex known; many mixotrophs	Euglena; relatives of trypanosomes
Chlorarachniophytes	Rhizaria (Cercozoa); secondary green plastid	Chl a and b; 4 membranes with a nucleomorph (relic algal nucleus)	Polysaccharide (β-1,3-glucan type) outside plastid	Marine amoebae with net-like pseudopods; some flagellate stages	Chlorarachnion, Bigelowiella
Cryptomonads (cryptophytes)	Cryptista; secondary red plastid	Chl a and c₂, phycobilins inside thylakoid lumen, alloxanthin; 4 membranes with a nucleomorph	Starch between the 2nd and 3rd membranes; protein periplast	Two-flagellate unicells with ejectisomes	Cryptomonas, Guillardia; a prime zooplankton food
Haptophytes and coccolithophores	Haptophyta; secondary red plastid	Chl a, c, fucoxanthin; 4 membranes, no nucleomorph	Chrysolaminarin; scales, calcite coccoliths in coccolithophores	Unicells with two flagella plus a haptonema	Emiliania huxleyi (blooms seen from space); ancient coccolithophores made chalk such as the White Cliffs of Dover, Phaeocystis, toxic Prymnesium
Dinoflagellates	Alveolata; plastids mostly secondary red (some replaced)	Chl a and c₂, peridinin; usually 3 membranes; about half have no plastid	Starch in cytoplasm; cellulose plates (thecae) inside alveoli, or naked	Two flagella, one in a girdle groove and one trailing; dinokaryon (always-condensed chromosomes); haplontic; resting cysts	Karenia brevis (Florida red tide), Alexandrium (paralytic shellfish poisoning), bioluminescent Noctiluca, coral zooxanthellae (Symbiodinium; bleaching)
Diatoms	Bacillariophyceae, stramenopiles (Ochrophyta); secondary red plastid	Chl a and c, fucoxanthin; 4 membranes (outer one joined to nuclear envelope)	Chrysolaminarin and oils; silica frustule of two overlapping halves	Centric (radial) and pennate (bilateral; raphe lets them glide); diplontic; cells shrink each division until an auxospore restores size	About 20% of Earth's photosynthesis; diatomaceous earth; domoic acid from Pseudo-nitzschia; used in forensics (drowning)
Brown algae	Phaeophyceae, stramenopiles	Chl a and c, fucoxanthin; 4 membranes	Laminarin and mannitol; cellulose plus alginates and fucoidan	Multicellular, almost all marine; holdfast, stipe, blades, air bladders; kelps: big sporophyte, microscopic gametophyte; Fucus diplontic; sperm with two side flagella	Giant kelp (Macrocystis), Laminaria, bull kelp, rockweed (Fucus), Sargassum; alginate thickens ice cream; kelp "trumpet hyphae" conduct sugars
Golden algae	Chrysophyceae, stramenopiles	Chl a and c, fucoxanthin; 4 membranes	Chrysolaminarin and oils; naked, silica scales or a lorica	Mostly freshwater flagellates and colonies; silica-walled resting cysts; many mixotrophs	Dinobryon, Synura, Mallomonas
Yellow-green algae	Xanthophyceae, stramenopiles	Chl a and c; little or no fucoxanthin, so yellow-green; 4 membranes	Oil droplets (chrysolaminarin reported); cellulose walls, often in two overlapping halves	Filaments and coenocytes; unequal flagella on zoospores	Vaucheria (coenocytic "water felt", oogamous), Tribonema, Botrydium
Oomycetes (for contrast)	Stramenopiles, not true fungi	No plastid; heterotrophs	Cellulose (and β-glucan) walls, not chitin	Diploid coenocytic filaments; swimming zoospores; oospores	Phytophthora infestans (potato late blight), Pythium (damping-off), downy mildews
Liverworts	Phylum Marchantiophyta; bryophytes	Chl a and b; 2 membranes (all land plants)	Starch; cellulose; unique oil bodies	Gametophyte dominant: thallus or leafy; one-celled rhizoids; no stomata; short-lived capsule with elaters; gemma cups	Marchantia, Riccia; once often placed as the earliest-diverging land plants; now usually grouped with mosses within monophyletic bryophytes
Mosses	Phylum Bryophyta	Same as all land plants	Starch; cellulose	Leafy gametophyte, multicellular rhizoids, protonema; sporophyte with foot, seta, capsule, peristome, calyptra; stomata on capsule	About 12,000 species; Sphagnum (peat; dead hyaline cells hold water; acidifies bogs), Polytrichum (hydroids and leptoids)
Hornworts	Phylum Anthocerotophyta	Often one large chloroplast per cell with a pyrenoid (unique in land plants)	Starch; cellulose	Thalloid gametophyte; horn-shaped sporophyte grows from a basal meristem; stomata; Nostoc in mucilage cavities	Anthoceros; may be sister to mosses plus liverworts
Rhyniophytes †	Early polysporangiophytes (Silurian to Devonian)	Presumed as land plants	Lignified or simple conducting cells	Leafless, rootless, forking stems with terminal sporangia; homosporous	Cooksonia (Silurian, about 430 Ma; among the first vascular plants), Rhynia, Aglaophyton (Rhynie chert, Scotland, about 407 Ma)
Zosterophylls †	Lycophyte relatives (Devonian)	Presumed as land plants	Tracheids	Leafless stems; kidney-shaped sporangia on the sides of stems	Zosterophyllum; Asteroxylon of the Rhynie chert is an early lycophyte with leaf-like enations
Club mosses	Lycopodiaceae, phylum Lycopodiophyta	Same as all land plants	Starch; cellulose, lignin	Microphylls; dichotomous branching; sporangia on sporophylls, often in strobili; homosporous; long-lived subterranean gametophytes with fungi	Lycopodium, Huperzia, ground pine (Diphasiastrum); flammable spores were flash powder
Spike mosses and quillworts	Selaginellaceae and Isoetaceae, Lycopodiophyta	Same	Starch; cellulose, lignin	Heterosporous (micro- and megaspores); a small ligule on each leaf	Resurrection plant (Selaginella lepidophylla); Isoetes (aquatic; some do CAM; secondary growth)
Tree lycopsids †	Lepidodendrales, Lycopodiophyta (Carboniferous)	Presumed as land plants	Lignified, thick bark	Trees to about 40 m; diamond leaf scars; Stigmaria rooting systems; heterosporous, some seed-like	Lepidodendron, Sigillaria; major coal formers of the coal swamps
Trimerophytes †	Euphyllophyte grade (Devonian)	Presumed as land plants	Tracheids	Main axis with side branches (overtopping), terminal sporangia; homosporous	Psilophyton; thought to be near the ancestry of ferns and seed plants
Leptosporangiate ferns	Polypodiidae, monilophytes	Same as all land plants	Starch; cellulose, lignin	Megaphyll fronds, fiddleheads, rhizomes; sori, indusium; sporangium from one cell with an annulus; homosporous; free-living prothallus	Over 90% of fern species (about 11,000); bracken, Boston fern, tree ferns
Water ferns	Salviniales (leptosporangiate)	Same	Starch; cellulose	Heterosporous; spores in sporocarps	Azolla (hosts N-fixing Anabaena; rice green manure), Salvinia (invasive), Marsilea (four-leaf "clover")
Whisk ferns and adder's tongues	Psilotales and Ophioglossales (eusporangiate ferns)	Same	Starch; cellulose, lignin	Thick-walled eusporangia; subterranean, fungus-fed gametophytes; Psilotum has no roots or true leaves, forked stems and three-lobed synangia	Psilotum, Tmesipteris; adder's tongue (Ophioglossum, very high chromosome number), moonworts (Botrychium)
Marattioid ferns	Marattiales (eusporangiate)	Same	Starch; cellulose, lignin	Huge fronds with fleshy stipules; large sporangia in sori, fused into synangia in Marattia and Danaea but free in Angiopteris	Angiopteris, Marattia; tropical; an ancient lineage
Horsetails	Equisetales (Equisetidae), monilophytes	Same	Starch; cellulose with silica	Jointed, hollow, ribbed stems; whorls of small fused scale leaves; strobili; spores with elaters; homosporous	One living genus, Equisetum ("scouring rush"); extinct tree-sized Calamites † of coal swamps
Progymnosperms †	Late Devonian	Presumed as land plants	Secondary xylem like conifer wood	Woody trees reproducing by spores (some heterosporous), no seeds	Archaeopteris, the first forest-forming trees; link between ferns and seed plants
Seed ferns † ("pteridosperms")	Paraphyletic early seed plants (Late Devonian to Mesozoic)	Presumed as land plants	Wood	Fern-like fronds that bore seeds; the first seed plants	Elkinsia (earliest seeds, about 365 Ma), Medullosa, Lyginopteris; Glossopteris (Permian Gondwana; evidence for continental drift)
Cordaitales †	Coniferophyte relatives (Carboniferous to Permian)	Presumed as land plants	Wood	Tall trees with long strap-like, parallel-veined leaves; loose cones	Cordaites; related to the ancestors of conifers
Bennettitales † (cycadeoids)	Mesozoic seed plants (Triassic to Cretaceous)	Presumed as land plants	Wood	Cycad-like leaves and trunks; many had bisexual, flower-like cones	Cycadeoidea, Williamsonia; once proposed as close angiosperm relatives
Cycads	Phylum Cycadophyta	Same as all land plants	Starch; cellulose, lignin	Palm-like, slow-growing; dioecious; large cones; coralloid roots with cyanobacteria; flagellated sperm; archegonia	Cycas revoluta (sago palm; toxic to pets), Zamia (coontie, Florida's native cycad); toxins cycasin and BMAA
Ginkgo	Phylum Ginkgophyta	Same	Starch; cellulose, lignin	Deciduous tree; fan leaves with forking veins; short shoots; dioecious; flagellated sperm (Hirase, 1896); fleshy seeds smell of butyric acid	Ginkgo biloba only; "living fossil"; plant male trees on streets; survived Hiroshima
Pine family	Pinaceae, phylum Coniferophyta	Same	Starch; cellulose, lignin; resin ducts	Needles (pines in bundles called fascicles); woody seed cones with two ovules per scale; pollen usually with air sacs (absent in larch and Douglas-fir); about 15 months from pollination to fertilization in pines	Pines, spruces, firs, hemlocks, Douglas-fir, larches (deciduous); bristlecone pine (oldest non-clonal trees, over 4,800 years)
Cypress family and other conifers	Cupressaceae, Taxaceae, Podocarpaceae, Araucariaceae	Same	Starch; cellulose, lignin	Scale or needle leaves; small woody or berry-like cones; yews have a single seed in a red aril	Coast redwood (tallest tree), giant sequoia (most massive), dawn redwood and bald cypress (deciduous), junipers (gin berries); Pacific yew (taxol), monkey puzzle, Wollemi pine
Gnetophytes	Phylum Gnetophyta	Same	Starch; cellulose, lignin	Vessels in xylem; compound strobili; a form of double fertilization (Ephedra, Gnetum) without true endosperm; Gnetum and Welwitschia lack archegonia	Ephedra (ephedrine; Mormon tea), Gnetum (broad-leaved tropical vines and trees), Welwitschia (two leaves for life; Namib Desert)
ANA grade	Amborellales, Nymphaeales, Austrobaileyales; earliest angiosperm branches	Same	Starch; cellulose, lignin	Small flowers with spiral, often many parts; Amborella lacks vessels (tracheids only)	Amborella trichopoda (New Caledonia; sister to all other flowering plants), water lilies (Nymphaea, giant Victoria), star anise (Illicium)
Magnoliids	Clade of Magnoliales, Laurales, Piperales, Canellales	Same	Starch; cellulose, lignin; aromatic oil cells	Single-aperture (monosulcate) pollen; often many free, spirally arranged flower parts and undifferentiated tepals	Magnolia, tulip tree, pawpaw, nutmeg; avocado, cinnamon, bay laurel, sassafras; black pepper; about 10,000 species
Ceratophyllum and Chloranthales	Small early mesangiosperm lineages	Same	Starch; cellulose	Coontail is submerged and rootless with tiny unisexual flowers; Chloranthaceae have tiny reduced flowers	Hornwort or coontail (Ceratophyllum; not the bryophyte hornworts), Chloranthus
Monocots	Clade Monocotyledons (Liliopsida)	Same	Starch; cellulose; commelinids (grasses, palms) add UV-fluorescent ferulic acid to walls	One cotyledon; parallel veins; parts in threes; scattered vascular bundles; fibrous adventitious roots; no true secondary growth; monosulcate pollen	About a quarter of angiosperms; grasses, orchids, lilies, palms, sedges, bromeliads, gingers, aroids, duckweeds; sweet flag (Acorus) branches first
Early-diverging eudicots	Ranunculales, Proteales and others	Same	Starch; cellulose, lignin	Tricolpate pollen (three apertures) marks all eudicots; often many free floral parts	Buttercups, columbine, poppies, barberry; sacred lotus (Nelumbo), sycamores and plane trees, Protea
Caryophyllales	Order in core eudicots	Same	Starch; cellulose; most use betalain pigments instead of anthocyanins	Many succulents, halophytes and carnivores; unusual anomalous secondary growth in some	Cacti, carnations, spinach, beets, amaranth, four-o'clocks; sundews (Drosera), Venus flytrap, pitcher plants (Nepenthes)
Rosids	Large clade of core eudicots	Same	Starch; cellulose, lignin	Mostly free petals; some with nitrogen-fixing root nodules, all within one "nitrogen-fixing clade" (legumes, Alnus)	Legumes, roses, mustards, maples, oaks, citrus, cucurbits, grapes, Arabidopsis
Asterids	Large clade of core eudicots	Same	Starch; cellulose, lignin	Mostly fused petals (sympetalous), often one ovule wall layer; iridoid compounds common	Sunflowers and daisies, tomatoes and potatoes, mints, coffee, carrots, olives, blueberries, morning glories

Woody vs. herbaceous and life spans

Woody plants make wood (secondary xylem) from a vascular cambium and keep their stems above ground from year to year: trees (one main trunk), shrubs (several stems from the base) and woody vines (lianas). Herbaceous plants have soft, green, non-woody stems that die back to the ground at the end of the season, though herbaceous perennials survive underground. Vines climb or trail on supports by twining, tendrils or roots; they may be woody (grape, wisteria) or herbaceous (morning glory). Ecologists divide herbaceous plants into graminoids (grass-like plants: grasses, sedges and rushes) and forbs (broad-leaved, non-grass-like herbs such as wildflowers). Growth habit words: upright, climbing, creeping (growing horizontally along the ground), rosette.

Deciduous plants drop all their leaves for an unfavorable season (winter or a dry season) and regrow them; evergreen plants keep leaves year-round, replacing them gradually. Many deciduous trees are angiosperms and many evergreens are conifers, but there are exceptions both ways (evergreen hollies and live oaks; deciduous larches).

Record holders tests like: the oldest known individual tree is a Great Basin bristlecone pine (Pinus longaeva, "Methuselah", over 4,800 years old); the largest tree by volume is the giant sequoia General Sherman; the tallest is a coast redwood (about 116 m); the most massive clonal organism is Pando, a grove of genetically identical quaking aspen in Utah joined by one root system; the smallest flowering plant is watermeal (Wolffia), a rootless floating duckweed relative (duckweed, Lemna, is a different genus that does have roots); the largest single flower is Rafflesia arnoldii.

Naming and classification

Binomial nomenclature, popularized by Carl Linnaeus (Species Plantarum, 1753, the official starting point for plant names), gives every species a two-part Latin name: the genus (capitalized) and the specific epithet (lowercase), both italicized, as in Zea mays (corn) or Helianthus annuus (common sunflower). A name may be followed by the author who published it ("L." for Linnaeus). Names are governed by the International Code of Nomenclature for algae, fungi, and plants; each name is tied to a type specimen in a herbarium. Hybrids carry a multiplication sign (Mentha × piperita, peppermint); cultivars carry a name in single quotes (Malus domestica 'Gala'); orchid hybrid groups are registered as a grex.

Plant taxonomy has three core tasks: identification (deciding what a specimen is), nomenclature (giving it the correct name) and classification (placing it in a hierarchy of related groups), resting on careful description. The hierarchy, most to least inclusive: kingdom, phylum (botanists say division), class, order, family, genus, species. Ranks above genus have standard endings in plants: division -phyta, class -opsida, order -ales, family -aceae. Eight families also keep older, conserved names: Gramineae (Poaceae), Leguminosae (Fabaceae), Compositae (Asteraceae), Cruciferae (Brassicaceae), Umbelliferae (Apiaceae), Labiatae (Lamiaceae), Palmae (Arecaceae) and Guttiferae (Clusiaceae).

Classification systems moved from artificial to natural to phylogenetic. Theophrastus grouped plants by growth form (trees, shrubs, subshrubs, herbs). Linnaeus's sexual system was artificial: it sorted flowering plants by the number and arrangement of stamens and pistils. Natural systems (de Jussieu, de Candolle, Bentham and Hooker) grouped plants by overall similarity; evolutionary systems followed (Engler and Prantl, Cronquist, Takhtajan). Today's Angiosperm Phylogeny Group system (APG IV, 2016) is built from DNA sequences and recognizes 64 orders and 416 families. Cladistic terms: a clade or monophyletic group contains an ancestor and all its descendants; a paraphyletic group contains an ancestor and only some descendants ("dicots" and the green algae are examples; older texts also call bryophytes paraphyletic, though recent DNA studies mostly find them monophyletic); a polyphyletic group gathers organisms from different ancestors ("algae" as a whole); a synapomorphy is a shared derived trait that defines a clade (double fertilization for angiosperms). Phylogenetic trees are built from shared heritable characters: DNA and protein sequences and morphological (and fossil) traits, analyzed for synapomorphies; geographic location or overall similarity alone does not establish relationships. A dichotomous key identifies a specimen by a series of paired, mutually exclusive choices.

Plant families to know

Identification questions name a family, a genus or a common plant and ask you to match them. The families below cover most of what tests ask; learn the field marks in the third column.

ReferenceCommon plant families· 28 rows

M = monocot. Placentation and fruit types are explained under Flowers and Fruits and seeds.

28 rows

Family (older name)	Members	Field marks
Poaceae (Gramineae), grasses, M	Wheat, rice, corn, oats, barley, bamboo, sugarcane, lawn grasses	Hollow round stems with solid nodes; leaf sheath and ligule; tiny wind-pollinated flowers in spikelets; fruit a caryopsis (grain); embryo with a scutellum
Fabaceae (Leguminosae), legumes	Peas, beans, soybean, peanut, clover, alfalfa, lupines (Texas bluebonnet), mesquite, redbud, wisteria, black locust	Often compound leaves; in most, "butterfly" (papilionaceous) flowers with banner, wings and keel; fruit a legume (pod); root nodules with nitrogen-fixing rhizobia in most; marginal placentation
Rosaceae, rose family	Rose, apple, pear, cherry, peach, plum, almond, strawberry, raspberry, hawthorn	Five petals and many stamens; hypanthium (floral cup); stipules; fruits include pomes, drupes, aggregates and accessory fruits
Asteraceae (Compositae), daisy family	Sunflower, daisy, dandelion, lettuce, marigold, zinnia, chrysanthemum, ragweed, artichoke	A head (capitulum) of many tiny florets (ray and disk) that looks like one flower; fruit a cypsela (achene-like), often with a pappus for wind; basal placentation; the largest or second-largest flowering-plant family
Solanaceae, nightshade family	Tomato, potato, eggplant, peppers, tobacco, petunia, deadly nightshade, ground cherry, buffalo bur	Five fused petals; often toxic alkaloids (solanine, nicotine, atropine); fruit a berry or capsule; ovary of two carpels set obliquely; axile placentation
Brassicaceae (Cruciferae), mustard family	Cabbage, broccoli, cauliflower, kale, Brussels sprouts, kohlrabi (all Brassica oleracea), mustard, radish, turnip, Arabidopsis	Four petals in a cross; six stamens (four long, two short); fruit a silique (or a short silicle); pungent glucosinolates; parietal placentation
Apiaceae (Umbelliferae), carrot family	Carrot, celery, parsley, parsnip, dill, fennel, coriander, poison hemlock	Flowers in umbels; often hollow stems; aromatic; fruit a schizocarp that splits in two
Lamiaceae (Labiatae), mint family	Mint, basil, sage (Salvia), rosemary, lavender, thyme, oregano	Square stems, opposite leaves, aromatic oils, two-lipped flowers
Cucurbitaceae, gourd family	Squash, pumpkin, cucumber, melons, watermelon, gourds, luffa (loofah)	Climbing vines with tendrils; separate male and female flowers (usually monoecious); fruit a pepo
Liliaceae (narrow sense), lily family, M	Lilies, tulips, trout lily	Showy flowers with six tepals in threes; bulbs; superior ovary. Onions and garlic are now in Amaryllidaceae, asparagus and hostas in Asparagaceae
Amaryllidaceae, M	Onion, garlic, leek, chives, daffodil, amaryllis	Bulbs; flowers often in umbels; onion smell in Allium
Orchidaceae, orchids, M	Orchids, vanilla	The largest or second-largest family; zygomorphic flowers with a lip (labellum) and a column of fused stamens and pistil; pollen in packets (pollinia); dust-like seeds that need mycorrhizal fungi to germinate; many epiphytes
Arecaceae (Palmae), palms, M	Coconut, date palm, oil palm	Woody monocots with no vascular cambium; large fan or feather leaves
Bromeliaceae, M	Pineapple, Spanish moss, many epiphytes	Leaf rosettes that hold water ("tanks"); CAM in many
Cactaceae, cacti	Cacti, prickly pear	Spines (modified leaves) grow from areoles, the feature that marks a cactus; succulent stems; CAM; almost all native to the Americas
Fagaceae, beech family	Oaks (Quercus), beeches (Fagus), chestnuts	Nuts in a cup or spiny husk (acorns); catkins
Betulaceae, birch family	Birches (Betula), alders, hazelnuts	Catkins; alders fix nitrogen with Frankia bacteria
Juglandaceae	Walnuts (Juglans), pecans, hickories	Pinnately compound leaves; nuts in a husk; black walnut's juglone
Sapindaceae	Maples (Acer), buckeyes, lychee	Maples and buckeyes have opposite leaves; maples have paired samaras
Salicaceae	Willows (Salix), poplars, aspens, cottonwoods (Populus)	Dioecious; catkins; salicin in the bark
Rutaceae, citrus family	Orange, lemon, lime, grapefruit	Aromatic oil glands dotting the leaves; fruit a hesperidium
Moraceae, mulberry family	Fig, mulberry, breadfruit, rubber plant (Ficus elastica)	Milky latex; multiple fruits (the fig is a syconium)
Malvaceae, mallow family	Cotton, hibiscus, okra, cacao, durian	Stamens often fused into a tube around the style (hibiscus, cotton)
Euphorbiaceae, spurge family	Poinsettia, cassava, castor bean, rubber tree (Hevea)	Often milky, toxic latex; small unisexual flowers (in Euphorbia, such as poinsettia, grouped in a cup-like cyathium)
Ericaceae, heath family	Blueberry, cranberry, azalea, rhododendron	Acid-soil plants with special (ericoid) mycorrhizae
Anacardiaceae, cashew family	Cashew, mango, pistachio, poison ivy, sumac	Resinous sap that can irritate skin (urushiol); often dioecious or with mixed flower types
Pinaceae (gymnosperm)	Pines (Pinus), spruces, firs, larches	Needles (pines in bundles called fascicles); woody seed cones
Others in plant-ID lists	Carnation and pinks (Dianthus, Caryophyllaceae), poppy (Papaver, Papaveraceae), evening primrose (Oenothera, Onagraceae), passionflower (Passifloraceae), violets and pansies (Violaceae), verbenas (Verbenaceae), honeysuckles (Lonicera, Caprifoliaceae), snapdragon (Plantaginaceae), sweet potato and morning glory (Convolvulaceae), eucalyptus (Myrtaceae), buttercups (Ranunculaceae)

The spiderwort family (Commelinaceae) is another frequent ID group: spiderworts (Tradescantia, including the houseplant often sold as wandering Jew, T. zebrina) and dayflowers (Commelina, such as whitemouth or erect dayflower, C. erecta), whose flowers open for a single morning with two showy blue petals and one small one. Regional identification lists, especially at Texas tournaments, pair scientific and common names of native wildflowers. Examples with their families: Texas bluebonnet (Lupinus texensis, Fabaceae; the state flower), Indian paintbrush (Castilleja, Orobanchaceae), Indian blanket (Gaillardia pulchella, Asteraceae), Mexican hat (Ratibida columnifera, Asteraceae), black-eyed Susan (Rudbeckia hirta, Asteraceae), clasping coneflower (Dracopis amplexicaulis, Asteraceae), purple coneflower (Echinacea, Asteraceae), thistles (Cirsium, Asteraceae), desert marigold (Baileya multiradiata, Asteraceae), eryngo or button snakeroot (Eryngium, Apiaceae), Texas bluebell (Eustoma, Gentianaceae) and rose gentians (Sabatia, Gentianaceae), pink evening primrose (Oenothera speciosa, Onagraceae), winecup (Callirhoe, Malvaceae), mealy sage (Salvia farinacea, Lamiaceae), horsemint (Monarda citriodora, Lamiaceae), coral bean (Erythrina herbacea, Fabaceae), honey mesquite (Prosopis glandulosa, Fabaceae), evening rain lily, also called autumn zephyr lily (Cooperia drummondii, now Zephyranthes drummondii, Amaryllidaceae), coral honeysuckle (Lonicera sempervirens, Caprifoliaceae), milkweeds (Asclepias, Apocynaceae), prickly pear (Opuntia, Cactaceae), yuccas and agaves (Asparagaceae), wild pansy and violets (Viola, Violaceae), buffalo bur (Solanum rostratum, Solanaceae; doves and quail eat its seeds) and lantana (Lantana, Verbenaceae). Many of these wildflowers have become garden and florist plants: Texas bluebell (Eustoma) is the cut-flower lisianthus, and purple coneflower, black-eyed Susan, gaillardia, yarrow, salvias and milkweeds are staples of pollinator gardens and xeriscapes. Endangered Texas plants include Texas wild rice (Zizania texana) and the star cactus (Astrophytum asterias), both federally listed.

Genus names tests often expect: Pelargonium (the garden geranium; true Geranium is cranesbill), Acer (maple; a stylized maple leaf is on Canada's flag), Quercus (oak), Juglans (walnut), Pinus (pine), Betula (birch), Fagus (beech), Salix (willow), Populus (poplar, aspen), Dianthus (carnation), Helianthus (sunflower), Papaver (poppy), Taraxacum (dandelion), Malus (apple), Prunus (cherry, plum, peach, almond), Rosa (rose), Solanum (tomato, potato, eggplant), Phaseolus vulgaris (common and green bean), Pisum sativum (garden pea), Triticum (wheat), Oryza sativa (rice), Gossypium (cotton), Coffea (coffee), Camellia sinensis (tea), Theobroma cacao (chocolate), Nicotiana (tobacco), Vitis (grape).

Monocots vs. dicots

The traditional "dicots" are not one natural group: most are eudicots (a monophyletic group with three-pored pollen), and a few early-branching lineages (magnolias, water lilies, laurels, black pepper) sit outside both. So monocots and eudicots are each monophyletic, while "dicots" in the old sense are paraphyletic. Monocots are not eudicots. Tests usually use "dicot" in the traditional sense. Among crops, the monocots are the grasses and grains (corn, wheat, rice, oats, barley, sugarcane), onions, garlic and leeks, asparagus, bananas, pineapple, ginger, yams and coconut and date palms; nearly every other vegetable and fruit is a eudicot, including spinach and beets (Amaranthaceae), lettuce, beans, tomatoes, potatoes, carrots and apples. A useful field rule: count the petals (threes for monocots, fours or fives for dicots) and look at the veins. Grass-like monocots are told apart with the rhyme "sedges have edges, rushes are round, grasses have joints": sedges (Cyperaceae, such as papyrus and nutsedge) have solid, usually triangular stems with leaves in three ranks; rushes (Juncaceae) have round, often pith-filled stems; grasses (Poaceae) have round, usually hollow stems with solid, swollen nodes and leaves in two ranks.

Photosynthesis and respiration

Photosynthesis converts light energy into chemical energy. Chemically it is a redox process: water is oxidized (it loses electrons and releases O₂) and CO₂ is reduced to carbohydrate (it gains electrons, carried by NADPH). Almost all the carbon in a plant comes from the air through the stomata, not from the soil. Photosynthesis by plants, algae and cyanobacteria is also the source of essentially all the O₂ in the atmosphere.

The chloroplast

Photosynthesis in plants happens in chloroplasts, mostly in the palisade mesophyll of leaves (a single leaf cell may hold dozens). A chloroplast has a double-membrane envelope around a fluid stroma, in which sits a third membrane system, the thylakoids. Thylakoids are flattened sacs stacked like coins into grana (singular granum) and joined by unstacked stroma lamellae; the space inside each sac is the lumen. The light reactions run in the thylakoid membranes; the Calvin cycle runs in the stroma, which also holds the chloroplast's own circular DNA (on the order of 100 genes; most chloroplast proteins are now encoded in the nucleus), its bacteria-like 70S ribosomes, and starch grains.

Those bacterial features are the evidence for the endosymbiotic theory: chloroplasts descend from a cyanobacterium engulfed by a eukaryotic cell, just as mitochondria descend from an engulfed aerobic bacterium (an alpha-proteobacterium). The evidence: two membranes, their own circular DNA without histones, 70S ribosomes, division by binary fission (chloroplasts are never built from scratch, only by dividing), bacterial size, and gene sequences closest to cyanobacteria. Glaucophyte algae still keep a layer of bacterial peptidoglycan between their chloroplast membranes. Endosymbiosis is still happening: in 2024 researchers described the nitroplast, a nitrogen-fixing organelle in the marine alga Braarudosphaera bigelowii that evolved from an engulfed cyanobacterium (UCYN-A). This single "primary" endosymbiosis gave rise to the glaucophytes, red algae and green algae (with land plants); brown algae, diatoms, euglenoids and dinoflagellates got their chloroplasts secondhand, by engulfing a red or green alga (secondary endosymbiosis), so their chloroplasts have three or four membranes.

Light and pigments

Only photosynthetically active radiation (PAR, 400 to 700 nm, the visible band) drives photosynthesis; it is a little under half (about 45%) of the energy in sunlight. Shorter wavelengths carry more energy per photon:

Chlorophyll absorbs blue and red strongly and absorbs green (about 500 to 600 nm) least, so more green light is reflected and transmitted than other colors, which is why leaves look green. (A leaf still absorbs much of the green light, which drives photosynthesis in deeper cell layers.) Grow lights therefore emphasize red and blue. A plot of absorption against wavelength is an absorption spectrum; a plot of photosynthetic rate against wavelength is an action spectrum. In 1882 Theodor Engelmann made the first action spectrum by shining a spectrum of light along a filamentous green alga (Cladophora) and watching aerobic bacteria crowd around the parts lit by blue and red light, where the most O₂ was released.

Light is also needed to make chlorophyll in the first place: seedlings grown in darkness are pale yellow and spindly (etiolated) because in flowering plants one step of chlorophyll synthesis needs light, and many light-activated genes stay off. Leaves can also turn yellow (chlorotic) from too little light or from nitrogen, magnesium or iron shortage.

The light-dependent reactions

The light reactions run in the thylakoid membranes and turn light energy into the two energy carriers the Calvin cycle needs, ATP and NADPH, releasing O₂ as a by-product.

1. Light harvesting. Hundreds of pigment molecules in light-harvesting (antenna) complexes absorb photons and pass the energy inward to a reaction center, a special pair of chlorophyll a molecules. The antenna itself has no reaction center; it only funnels energy. Light-harvesting complexes are pigment-binding proteins holding chlorophyll a, chlorophyll b and carotenoids. PSII relies on a large, mobile outer antenna (LHCII, the most abundant membrane protein in chloroplasts), while PSI has a large built-in core antenna plus a smaller set of LHCI proteins.
2. Photosystem II (PSII) acts first. Its reaction center, P680 (it absorbs best at 680 nm), loses an excited electron to the primary acceptor. The oxygen-evolving complex, a cluster of four manganese ions and one calcium on the lumen side of PSII, refills P680 by splitting water (photolysis): 2 H₂O → 4 H⁺ + 4 e⁻ + O₂. The protons stay in the lumen. Manganese deficiency therefore stalls water splitting.
3. The electron passes along an electron transport chain: plastoquinone (PQ, a mobile carrier in the membrane) → the cytochrome b₆f complex (which pumps protons into the lumen) → plastocyanin (PC, a small copper protein in the lumen). (The cytochrome b₆f complex is the chloroplast's counterpart of mitochondrial Complex III, the cytochrome bc₁ complex.)
4. Photosystem I (PSI), with reaction center P700, absorbs a second photon and re-energizes the electron, which passes to ferredoxin (Fd, an iron-sulfur protein on the stroma side) and then to the enzyme ferredoxin-NADP⁺ reductase, which makes NADPH: NADP⁺ + 2 e⁻ + H⁺ → NADPH. NADP⁺ is the final electron acceptor.
5. Chemiosmosis. Water splitting and the PQ/cytochrome pump pile protons up in the lumen. They flow back to the stroma through ATP synthase, which makes ATP from ADP and phosphate (photophosphorylation). A poison that blocks ATP synthase leaves a large proton gradient but no ATP; an uncoupler, which lets protons leak across the membrane, collapses the gradient, so again no ATP is made.

Reasoning about blocked steps: a drug that blocks the cytochrome b₆f complex stops linear and cyclic flow and its proton pumping, so the lumen becomes less acidic (higher pH), the stroma less alkaline, and both ATP and NADPH fall; blocking photosystem I still lets PSII split water and evolve O₂ briefly until the chain backs up; electrons rerouted from ferredoxin back to plastoquinone (and so through cytochrome b₆f) behave like cyclic flow, adding ATP but no NADPH; an uncoupler collapses the gradient so electrons flow but no ATP is made. Plotted by energy, the path looks like a sideways Z (the Z-scheme): water (low energy) up to excited P680, down the chain, up again at P700, down to NADPH. Photosystem II comes before photosystem I in the electron path; the numbers only reflect the order of discovery. Moving one O₂-worth of electrons (four) through both photosystems takes about eight photons (four at each).

Cyclic electron flow uses PSI alone: electrons from ferredoxin pass back to plastoquinone, then through the cytochrome b₆f complex (which pumps protons) and plastocyanin, and return to P700. It pumps protons and makes ATP only, with no NADPH and no O₂. The Calvin cycle uses 3 ATP for every 2 NADPH, a little more ATP than linear flow supplies, and cyclic flow makes up the difference.

PSII sits mainly in the stacked grana, while PSI and ATP synthase sit mainly in the stroma lamellae and the edges of grana, where they face the stroma that holds their substrates (NADP⁺, ADP) and where their bulky stromal parts fit.

The Calvin cycle (light-independent reactions)

The Calvin cycle (also the Calvin-Benson-Bassham cycle, reductive pentose phosphate pathway, or the old "dark reactions", though it runs in the day because it depends on light-made ATP and NADPH and several of its enzymes are switched on by light) runs in the stroma in three phases:

1. Carbon fixation. RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) attaches CO₂ to the five-carbon sugar RuBP (ribulose-1,5-bisphosphate). The unstable six-carbon product splits at once into two molecules of the three-carbon 3-phosphoglycerate (3-PGA). This is why the pathway is called C₃. RuBisCO is slow, catalyzing only a few reactions per second, so it is often the rate-limiting step, and leaves make enormous amounts of it: RuBisCO is the most abundant protein on Earth. RuBisCO must first be activated: an activator CO₂ molecule (separate from the CO₂ it will fix) and Mg²⁺ bind a lysine in its active site (carbamylation), helped by the enzyme Rubisco activase, which clears inhibitory sugar phosphates from the active site and is itself switched on in light.
2. Reduction. ATP and NADPH convert 3-PGA to glyceraldehyde-3-phosphate (G3P, a triose phosphate). These steps run part of glycolysis in reverse, which is why the cycle is sometimes called a reversed glycolysis.
3. Regeneration. Most of the G3P is rearranged, using more ATP, back into RuBP so the cycle can continue.

Six turns fix six CO₂ into 12 G3P; 10 of them regenerate six RuBP and 2 leave the cycle. The direct carbohydrate product is G3P, not glucose. It is exported from the chloroplast through a triose phosphate/phosphate translocator (an antiporter that swaps each triose phosphate for an inorganic phosphate) and built into sucrose in the cytosol for transport, or kept in the chloroplast and built into starch for storage. Most fixed carbon ends up as sucrose, starch and cellulose, not free glucose. The Calvin cycle uses ATP and NADPH and returns ADP and NADP⁺ to the thylakoids; it makes neither.

Photorespiration, C₄ and CAM

RuBisCO can also grab O₂ instead of CO₂. That oxygenase reaction makes one 3-PGA and one two-carbon phosphoglycolate, which the plant must salvage through a pathway spread across the chloroplast, the peroxisome and the mitochondrion, releasing CO₂ and spending ATP. This photorespiration fixes no carbon and wastes energy, and it is common, not rare: it rises sharply when the leaf is hot and its stomata are closed (on hot, dry days, or under bright light with low CO₂), because O₂ from the light reactions builds up and CO₂ runs down inside the leaf, and because RuBisCO's preference for CO₂ over O₂ falls as temperature rises. C₃ plants in warm conditions can lose roughly a quarter of their fixed carbon this way.

C₄ and CAM plants avoid it by fixing CO₂ first with PEP carboxylase, an enzyme that adds bicarbonate (HCO₃⁻) to the three-carbon phosphoenolpyruvate (PEP) to make the four-carbon oxaloacetate. PEP carboxylase has a much higher affinity for CO₂ (as bicarbonate) than RuBisCO and does not react with O₂. The four-carbon acid (malate or aspartate) is later broken down to release CO₂ at high concentration around RuBisCO.

• C₄ (spatial separation). Mesophyll cells fix CO₂ with PEP carboxylase; malate or aspartate moves through plasmodesmata into the bundle-sheath cells, which wrap the veins in a wreath (Kranz anatomy, German for wreath); there it is decarboxylated, and the Calvin cycle runs on the concentrated CO₂. Pyruvate returns to the mesophyll and is turned back into PEP at a cost of ATP, so C₄ photosynthesis needs more ATP per CO₂ (about 5 instead of 3). It pays off in hot, bright, dry places (grasslands, savannas, warm-season crops) because stomata can stay narrower and photorespiration nearly disappears. C₄ examples: corn (maize), sugarcane, sorghum, millets, crabgrass, switchgrass, amaranth.
• CAM (temporal separation). Crassulacean acid metabolism (named for the stonecrop family, Crassulaceae) opens stomata at night, when air is cool and humid, fixes CO₂ with PEP carboxylase and stores it as malic acid in the vacuole (the leaf becomes sour by dawn). By day the stomata stay closed, malate releases CO₂ inside the leaf, and the Calvin cycle runs. Some plants switch between C₃ and CAM depending on conditions (facultative CAM): the common ice plant (Mesembryanthemum crystallinum) runs C₃ when watered and shifts to CAM under drought or salt stress. Under severe drought some CAM plants keep their stomata shut day and night and recycle their own respired CO₂ (CAM idling); not all CAM plants can do this. CAM gives the best water-use efficiency of the three and suits deserts and epiphytes: cacti, agave, pineapple, jade plant and other succulents, many orchids and bromeliads, and (only weakly) Welwitschia.
• C₃ is the ancestral, most common pathway (the large majority of plant species, commonly quoted at around 85 to 95%): wheat, rice, soybean, potato, spinach, most trees. It is efficient in cool, moist, moderately lit conditions.

Rates and limiting factors

The rate of photosynthesis depends on light intensity, CO₂ concentration and temperature (plus water and nutrients, which act through stomata and leaf chemistry). Whichever factor is in shortest supply sets the rate (Blackman's law of limiting factors): on a light-response curve the rate climbs with light, then levels off at the light saturation point, where CO₂ or temperature has become limiting. The light compensation point is the light level at which photosynthesis exactly balances respiration (net gas exchange zero); below it the plant loses carbon. Temperature gives a rise-and-fall curve because enzymes slow in the cold and denature or photorespire in heat. Rising atmospheric CO₂ can raise photosynthesis in C₃ crops (CO₂ fertilization) and lets plants partly close their stomata, which lowers transpiration.

Photosynthetic rate can be measured as O₂ released (bubbles from an aquatic plant such as Elodea, or leaf disks that float as O₂ fills their air spaces), CO₂ taken up, or dry mass gained. The overall efficiency is low: only a few percent of the light energy striking a leaf (typically quoted around 1 to 3% for crops over a season) ends up stored in sugar. The classic starch test shows where photosynthesis happened: keep a plant in the dark for a day to use up its starch (destarching), light it with part of a leaf covered (or use a variegated leaf), then boil the leaf, soak it in hot ethanol to remove chlorophyll, and add iodine. Only the parts that were lit and green turn blue-black, showing that light and chlorophyll are both needed.

Sun and shade leaves. Leaves that develop in full sun are smaller and thicker, with more layers of palisade cells, more RuBisCO, higher light saturation and compensation points and a higher chlorophyll a-to-b ratio. Shade leaves are larger and thinner, with more chlorophyll per reaction center, relatively more chlorophyll b (more antenna), and low compensation points, so they make a profit in dim light. A shade-adapted plant moved into full sun suffers photoinhibition (damage to PSII) and leaf scorch.

Cellular respiration

Respiration runs in every living plant cell, day and night, and releases the energy stored in sugar as ATP:

$$C_6H_{12}O_6 + 6\,O_2 \rightarrow 6\,CO_2 + 6\,H_2O + \text{energy (ATP and heat)}$$

Total yield is about 30 to 32 ATP per glucose by current estimates (older texts say 36 to 38, counting each NADH as 3 ATP and each FADH₂ as 2; newer texts use about 2.5 and 1.5). The CO₂ of respiration comes from pyruvate oxidation and the Krebs cycle; the CO₂ of photosynthesis enters through RuBisCO. Respiration is also the source of carbon skeletons for amino acids and other molecules.

Without O₂ (in waterlogged roots or germinating seeds under water), plant cells fall back on fermentation, mainly alcoholic (pyruvate → ethanol + CO₂), which regenerates NAD⁺ so glycolysis can continue but yields only 2 ATP per glucose; ethanol buildup is one reason flooding kills roots. Plant mitochondria also have a cyanide-resistant alternative oxidase that releases energy as heat instead of ATP; thermogenic flowers such as skunk cabbage and voodoo lily use it to warm their inflorescences and spread scent to pollinators. Respiration speeds up with temperature (roughly doubling per 10 °C, a Q₁₀ of about 2), which is why produce is stored cold, and many fruits show a burst of respiration (the climacteric) as they ripen.

Discovering photosynthesis

Genetics and reproduction

Mendelian genetics in plants

Gregor Mendel worked out the rules of inheritance (published 1866) with garden peas (Pisum sativum). Peas were a good choice: they grow quickly and give many offspring, have clear either-or traits (seed shape and color, flower color, pod shape and color, flower position, stem length: seven traits in all), come in true-breeding lines, and normally self-pollinate inside a closed flower but can be hand-crossed by removing a flower's anthers and dusting pollen from another plant's anthers onto its stigma.

Each trait is controlled by a gene with two alleles at the same locus on homologous chromosomes; one allele may be dominant over a recessive one. The genotype is the allele pair (TT, Tt, tt); the phenotype is the observable trait. Homozygous means two identical alleles; heterozygous, two different ones. Mendel's laws:

• Segregation: the two alleles of a gene separate during gamete formation (meiosis), so each gamete carries one.
• Independent assortment: alleles of different genes sort into gametes independently of each other (true for genes on different chromosomes or far apart on one).
• Dominance: in a heterozygote, the dominant allele determines the phenotype.

For two or more independent genes, find each gene's probability separately and multiply. A testcross with the homozygous recessive reveals an unknown genotype.

A Punnett square lays the possible gametes of one parent along the top and the other's down the side; each box is one equally likely offspring genotype. For Tt × Tt the boxes are TT, Tt, Tt and tt, giving the 1 : 2 : 1 genotype and 3 : 1 phenotype ratios.

Incomplete dominance gives a blended heterozygote: red × white snapdragons give all pink F₁ (0% red), and pink × pink gives 1 red : 2 pink : 1 white. In codominance both alleles show fully in the heterozygote (for example, a plant heterozygous for two forms of an enzyme shows both bands on a gel, or a flower with both red and white patches rather than pink). Epistasis, where one gene masks another, modifies the 9 : 3 : 3 : 1 ratio:

Genes close together on one chromosome are linked and tend to be inherited together; crossing over separates them at a frequency that grows with distance, which is how genes are mapped. DNA itself follows Chargaff's rule: the amount of A equals T and G equals C (because A pairs with T and G with C), so purines equal pyrimidines (A + G = T + C) in any species, though the A+T to G+C ratio varies. Barbara McClintock discovered transposons ("jumping genes") from mottled maize kernels (Nobel 1983).

Plant-specific genetics.

• Polyploidy (more than two chromosome sets) is common and often creates new species in one generation. Autopolyploids double their own genome; allopolyploids combine the genomes of two species after hybridization. Bread wheat is an allohexaploid built from three ancestral genomes (AABBDD, 2n = 6x = 42), which is why wheat genetics is notoriously hard; cultivated strawberries are octoploid; most bananas are sterile triploids. Seedless watermelons are triploids made by crossing a tetraploid with a diploid. Colchicine, which blocks spindle formation, is used to double chromosome numbers.
• Organelle inheritance. Chloroplast and mitochondrial genes are usually inherited only through the mother (the egg) in flowering plants. Conifers are the common exception: their chloroplasts are usually inherited through the pollen (paternally); mitochondria come from the mother in the pine family but through the pollen in the cypress family (including redwoods). Cytoplasmic male sterility, carried in mitochondria, is used to make hybrid seed; in 1970 the widely used Texas male-sterile cytoplasm made most U.S. corn susceptible to southern corn leaf blight.
• Ploidy of plant structures. Spores, pollen, the embryo sac and its egg, synergids and antipodal cells are haploid (n); the zygote, embryo, seed coat and fruit wall are diploid (2n, the seed coat and fruit being maternal tissue); endosperm is triploid (3n). In gymnosperms the seed's food store is the haploid female gametophyte.
• Self-incompatibility genes (the S-locus) block pollen carrying an S allele that matches the pistil's. In the nightshade and rose families the style makes S-RNases that destroy RNA in "self" pollen tubes; in the mustard family recognition happens at the stigma surface. In gametophytic self-incompatibility the pollen's own (haploid) S allele decides: S1 pollen landing on an S1S2 pistil is rejected because S1 matches, while S3 pollen on the same pistil grows normally. In sporophytic self-incompatibility (mustards) the pollen's behavior is set by the diploid genotype of the plant that made it. Self-incompatibility enforces outcrossing; in some species it weakens in older flowers that were never cross-pollinated, giving at least some seed.
• Model organisms. Arabidopsis thaliana (small genome, about six-week life cycle, self-pollinating, thousands of seeds, easy to transform) is the main model; rice, whose genome was the first crop genome sequenced (2002, finished 2005), and maize are the grass models.

Sexual reproduction in flowering plants

Pollination moves pollen from an anther to a receptive stigma; fertilization follows when the pollen tube delivers sperm to the ovule (see Flowers for the pollen tube and double fertilization). Self-pollination (pollen reaching a stigma of the same flower or plant) guarantees seed without a partner and is more common in angiosperms, with their bisexual flowers, than in gymnosperms; some violets even make closed, self-pollinating (cleistogamous) flowers. Cross-pollination mixes genes. Species that evolve toward regular self-pollination tend to lose the costly lures and rewards of outcrossers (the "selfing syndrome"): smaller, less showy flowers, less scent and reduced nectar, and fewer pollen grains per ovule. Plants avoid selfing and inbreeding depression by:

• Dioecy (separate male and female plants);
• Dichogamy: anthers and stigma mature at different times, either pollen first (protandry) or stigma first (protogyny), common in both bisexual flowers and monoecious plants;
• Herkogamy: anthers and stigma physically separated in the flower; heterostyly (pin and thrum flowers with long and short styles, as in primroses) is a special case;
• Self-incompatibility (above).

Flowers and pollinators shaped each other's traits over time (co-evolution). Pollinators besides insects include birds, bats, a few non-flying mammals and, rarely, lizards on islands. A gardener who wants no bees but still wants pollination should choose red, tubular, scentless flowers for hummingbirds. More generally, co-evolution is reciprocal evolutionary change in two interacting species, each adapting to the other: flowers and pollinators, plants and mycorrhizal fungi or rhizobia, and arms races between plant defenses and herbivore counter-defenses (milkweed toxins and monarchs). One species simply living on or near another, without each driving the other's evolution, is not co-evolution.

Seeds disperse by wind (dandelion pappus, maple samaras), water (coconut), animals (burrs, fleshy fruits eaten and passed) and explosive pods (Impatiens); see Fruits and seeds for the full table.

Asexual reproduction

Asexual reproduction makes clones by mitosis. Natural methods include stolons, rhizomes, tubers, bulbs and corms (see Stems), suckers from roots (aspen, raspberry), plantlets on leaves (Kalanchoe), gemmae in liverworts, fragmentation, and apomixis, seed formed without fertilization, so the "seedlings" are clones of the mother (dandelions, many citrus and blackberries). Gardeners add cuttings, layering, division, grafting and tissue culture (see Horticulture). The connected shoots of a clone (ramets, such as aspen trunks or strawberry plantlets) often stay physiologically integrated, sharing water, sugar and nutrients through their rhizomes or stolons so that a ramet in a good patch can support one in a poor patch. Clonal spread is fast and keeps a successful genotype, needs no pollinator or mate, and gives offspring a head start from the parent's food. But a clonal patch carries little genetic variation, so one disease or one environmental change can hit every plant the same way, and harmful mutations accumulate over many cell divisions because there is no sexual recombination to purge them. Salt-marsh cordgrass (Spartina), beach and dune grasses and reeds spread mainly this way, by rhizomes, building dense marshes and stabilizing dunes.

Paleobotany and plant evolution

Paleobotany is the study of fossil plants: identifying them, reconstructing whole plants from scattered organs, placing them in evolutionary history and using them to read past climates and environments (it does not attempt the impossible task of counting every extinct species, and it does not study ancient bacteria or animals). Plant fossils form in several ways: compressions (flattened organic films, common in shale and coal), impressions (an imprint with the tissue gone), petrifactions or permineralizations (minerals such as silica fill and preserve cells, as in petrified wood, coal balls and the Rhynie chert), casts and molds, and inclusions in amber (fossil resin). Fossil pollen and spores, protected by sporopollenin, survive almost anywhere; palynology uses them to reconstruct past vegetation and climate, and pollen diagrams from lake and bog sediments track how forests changed after the last ice age. In the lab, paleobotanists free cuticles and spores from rock with acids (maceration), make acetate peels of polished coal balls (etching the surface and lifting off a film of cells), and grind petrified material into thin sections for the microscope. Fossils are dated by the rocks around them (radiometric dating of volcanic layers, index fossils).

Read the timeline as a series of innovations, each solving a problem of life on land: the cuticle and stomata (drying out), sporopollenin-walled spores (surviving dry air), vascular tissue with lignin (standing tall and moving water), roots and leaves (capturing water and light), seeds (reproducing without swimming sperm and surviving dry spells), and flowers and fruits (recruiting animals to move pollen and seeds). Cell walls, by contrast, were inherited from algal ancestors and did not evolve on land. Partnerships with mycorrhizal fungi, already present in the earliest land plant fossils, helped them extract water and phosphorus from bare mineral soil.

Fossil leaves also record past climates: the stomatal index (stomata as a share of all epidermal cells) falls when CO₂ is high, so fossil cuticles track ancient CO₂; leaf-margin analysis uses the fact that the share of woody species with smooth (entire) leaf margins rises with mean annual temperature, while toothed margins dominate cool forests; larger leaves indicate wetter climates; and carbon-isotope ratios reveal C₃ versus C₄ vegetation. Two kinds of leaves. Microphylls, small leaves with a single unbranched vein, are found only in lycophytes and probably arose as outgrowths of the stem surface (the enation hypothesis). Megaphylls, leaves with branching veins, are found in ferns, horsetails and seed plants (gymnosperms and angiosperms) and evolved from flattened, webbed branch systems (the telome theory). Large megaphylls spread only in the Late Devonian and Carboniferous, after atmospheric CO₂ fell steeply (by roughly 90%): with less CO₂, leaves needed more stomata, and the extra transpiration cooled broad leaves enough to keep them from overheating.

Bryophytes fossilize poorly, but Triassic liverworts such as Naiadita lanceolata are known in detail. Living fossils are modern species little changed from fossil relatives: Ginkgo biloba (the sole survivor of an order that was diverse in the Jurassic), the dawn redwood (Metasequoia, known from fossils before living trees were found in China in the 1940s), the Wollemi pine (found in Australia in 1994), cycads, and horsetails.

History of botany

Expect matching and short-answer questions that pair a person with a discovery. Botany began as the study of useful and medicinal plants: before modern biology, much of it was the work of herbalists and physicians preparing plant drugs.

Ancient and medieval. Theophrastus classified plants by growth form into trees, shrubs, subshrubs and herbs, and also distinguished them by features such as habitat, wild versus cultivated, and evergreen versus deciduous. His books also record medicinal plants and the lore of root-gatherers, such as hellebore and birthwort (Aristolochia, named for its use in childbirth; it is now known to contain kidney-damaging aristolochic acids). Pliny the Elder's Natural History and Dioscorides' De Materia Medica carried classical plant knowledge forward. Through the European Middle Ages botany made little original progress: scholars mostly copied the ancient texts, while Islamic scholars preserved and extended them. Herbs were used in food and medicine for thousands of years, long before the 1800s (traditional systems such as Ayurveda in India and Chinese herbal medicine are ancient).

Renaissance and the age of exploration. Printing, accurate woodcut illustrations and specimens pouring in from voyages to the Americas and Asia revived botany. The German "fathers of botany", Otto Brunfels, Hieronymus Bock and Leonhart Fuchs, published illustrated herbals drawn from real plants; the first botanical gardens (Pisa and Padua, 1540s) and the first herbaria of pressed specimens date from this time. The microscope opened plant anatomy.

ReferencePeople in the history of botany· 33 rows

33 rows

Person	When	Contribution
Theophrastus	about 371-287 BCE	Student of Aristotle; wrote Enquiry into Plants and On the Causes of Plants; called the father of botany
Dioscorides	1st century CE	De Materia Medica, the standard guide to medicinal plants for some 1,500 years
Brunfels, Bock, Fuchs	1530s-1540s	Illustrated German herbals; Fuchs is honored in the name Fuchsia
Andrea Cesalpino	1583	Early classification based on fruits and seeds
Jan Baptista van Helmont	1600s	Willow experiment: the tree gained mass while the soil barely changed, so he credited water
Robert Hooke	1665	Named "cells" after viewing cork in Micrographia
Nehemiah Grew; Marcello Malpighi	1670s-1680s	Founders of plant anatomy (Grew is usually called the father of plant anatomy); Grew described flower parts and suggested stamens are male organs
Rudolf Jakob Camerarius	1694	Showed experimentally that plants reproduce sexually and need pollen to set seed
Stephen Hales	1727	Vegetable Staticks: measured transpiration and root pressure; founder of plant physiology
John Bartram	1728	Founded what is now the oldest surviving botanical garden in the United States, in Philadelphia
Carl Linnaeus	1753	Swedish; Species Plantarum, the starting point of binomial plant names; an artificial "sexual system" of classification; called the father of taxonomy
Joseph Priestley	1771	A plant "restored" air that a candle or mouse had used up
Jan Ingenhousz	1779	Showed that only the green parts of plants, and only in light, restore the air
Christian Konrad Sprengel	1793	Described how flowers are built for insect pollination (nectar guides, cross-pollination)
Alexander von Humboldt	Early 1800s	Founded plant geography: vegetation zones by latitude and altitude
Robert Brown	1827; 1831	Brownian motion (watching tiny particles released from pollen grains); described the cell nucleus in orchid cells
Matthias Schleiden	1838	All plant tissues are made of cells (cell theory, with Theodor Schwann for animals)
Charles Darwin	1859-1880	Evolution by natural selection; books on orchid pollination, carnivorous plants and plant movement
Gregor Mendel	1866	Laws of inheritance from pea crosses; rediscovered in 1900 by Hugo de Vries, Carl Correns and Erich von Tschermak
Charles and Francis Darwin	1880	Coleoptile tips sense light and send a signal that causes bending
Dmitri Ivanovsky; Martinus Beijerinck	1892; 1898	Tobacco mosaic disease agent passes through bacterial filters: the discovery of viruses
Sergei Nawaschin	1898	Discovered double fertilization
Christen Raunkiær	1904-1907	Life-form system based on where renewal buds survive the unfavorable season
Luther Burbank; George Washington Carver	Late 1800s-early 1900s	Burbank bred hundreds of cultivars (the Burbank potato, whose russet-skinned sport became the Russet Burbank); Carver promoted peanuts, sweet potatoes and crop rotation to restore Southern soils
Liberty Hyde Bailey	Late 1800s-early 1900s	American horticulturist at Cornell; coined "cultivar" (1923) and is called the father of American horticulture
Wightman Garner and Harry Allard	1920	Discovered photoperiodism, working with Maryland Mammoth tobacco and soybeans at the USDA
Frits Went	1926	Isolated the bending signal in agar blocks: auxin
Eiichi Kurosawa	1926	Showed the "foolish seedling" fungus secretes a growth substance: gibberellin
Nikolai Vavilov	1920s-1930s	Centers of origin of cultivated plants; built a huge seed collection
Melvin Calvin	1950s (Nobel 1961)	Traced carbon fixation with radioactive carbon-14: the Calvin cycle
Barbara McClintock	1940s-1950s (Nobel 1983)	Transposable elements in maize
Norman Borlaug	1960s (Nobel Peace 1970)	High-yield semi-dwarf wheat and the Green Revolution
Tu Youyou	1970s (Nobel 2015)	Artemisinin from sweet wormwood (Artemisia annua) against malaria

Plants in ecosystems

Energy and nutrient cycles

Plants are primary producers (autotrophs): almost all energy in terrestrial food webs enters through photosynthesis, so plants (and, in water, algae and cyanobacteria) sit at the base of nearly every ecological pyramid (deep-sea vent communities run on chemosynthesis instead). Gross primary production (GPP) is the total carbon fixed; net primary production (NPP) is what remains after the plants' own respiration, and NPP is what herbivores can eat. Global NPP is roughly 100 billion tonnes of carbon per year, split about evenly between land plants and ocean phytoplankton; marine phytoplankton (including cyanobacteria such as Prochlorococcus, and diatoms) therefore produce roughly half of the oxygen made each year. Phytoplankton includes both prokaryotic cyanobacteria (Prochlorococcus, the most abundant photosynthetic organism on Earth, and Synechococcus) and eukaryotic algae (diatoms, dinoflagellates, coccolithophores); tests may credit either "algae" or "cyanobacteria", so read the options. Only about 10% of the energy at one trophic level typically reaches the next, because most is lost as heat in respiration. Biomass is the total mass of living (or recently living) organic matter, a renewable source of food, fuel and materials. A bottom-up effect starts at the producers: a change in plant growth (drought, fertilizer, a crop failure) ripples up through every consumer level, whereas a top-down cascade starts with predators (or overhunting of them).

Carbon cycle. Photosynthesis (the Calvin cycle) pulls CO₂ from the air; respiration (pyruvate oxidation and the Krebs cycle), decomposition and burning return it. Forests and soils store large carbon pools, and coal, oil and gas are ancient plant and plankton carbon. Deforestation disrupts the cycle mainly by cutting photosynthetic uptake and releasing the carbon stored in wood and soil, so atmospheric CO₂ rises. Rising CO₂ can boost photosynthesis in C₃ crops (CO₂ fertilization) and lets plants use water more efficiently, but heat, drought and shifting growing zones (USDA hardiness zones are moving north) offset much of the gain. Ranked by size, Earth's carbon reservoirs are sedimentary rocks (limestone and organic carbon, by far the largest), then the oceans (mostly dissolved inorganic carbon in deep water), then soils and fossil-fuel deposits (similar in size; estimates vary on which is larger), the atmosphere and living vegetation; soils hold roughly two to four times as much carbon as either the atmosphere or all plant biomass.

Water cycle. Plants pull water from the soil and release it as vapor through transpiration; over land, transpiration makes up most of the water moving from the surface to the air, so clearing forests can reduce regional rainfall. Vegetation also slows runoff, lets rain soak in and holds soil.

Nitrogen cycle. Nitrogen is part of every amino acid, protein, nucleic acid and chlorophyll molecule, and it is the mineral nutrient plants need in the largest amount, yet plants cannot use atmospheric N₂. They absorb nitrogen as nitrate (NO₃⁻, most common) and ammonium (NH₄⁺) through their roots.

Nitrification is an oxidation that consumes oxygen and releases acid: NH₄⁺ + 1.5 O₂ → NO₂⁻ + 2 H⁺ + H₂O (ammonia oxidizers such as Nitrosomonas), then NO₂⁻ + 0.5 O₂ → NO₃⁻ (nitrite oxidizers such as Nitrobacter); the H⁺ released is one reason ammonium fertilizers acidify soil. The enzyme nitrogenase breaks the triple bond of N₂. Only prokaryotes (some bacteria and archaea) make nitrogenase; no plant can fix nitrogen itself, which is why fixation always involves bacterial partners (and why the algal nitroplast is remarkable). Nitrogenase appears to have a single evolutionary origin, and its core genes (the nif genes) are shared by all nitrogen fixers; related nif genes (nifE and nifN) help assemble the iron-molybdenum cofactor. It contains iron and molybdenum, uses a great deal of ATP (about 16 ATP per N₂), and is destroyed by oxygen, so legume nodules keep O₂ low with leghemoglobin, which makes them pink inside. In the legume partnership the plant supplies sugar and the bacteria supply fixed nitrogen (mutualism), which is why crop rotations follow legumes with nitrogen-hungry crops like corn. Haber-Bosch fertilizer now fixes about as much nitrogen as all natural processes on land; runoff of it causes eutrophication (algal blooms and dead zones), nitrate in groundwater and emissions of the greenhouse gas nitrous oxide.

Phosphorus cycle. Phosphorus has no significant gas phase; it comes from weathering rock, moves through soil and organisms, and is often the nutrient that limits growth. Plants absorb it as phosphate ions (H₂PO₄⁻ and HPO₄²⁻) dissolved in soil water. It binds tightly to soil particles and moves slowly, so plants rely on mycorrhizae and, in some families, cluster roots that release acids to free it. Phosphorus runoff is the main trigger of freshwater algal blooms.

Soil. Soil is weathered rock (mineral particles), organic matter (humus), water, air and organisms. Its layers (horizons) are the O horizon (leaf litter), A (topsoil, dark with humus, where most roots and soil life are), E (a leached zone in some soils), B (subsoil, where clay and minerals accumulate), C (weathered parent material) and R (bedrock). Particles are sorted by size: sand (0.05 to 2 mm, mostly quartz, silicon dioxide), silt (0.002 to 0.05 mm) and clay (under 0.002 mm). The soil texture triangle names a soil from its percentages of sand, silt and clay. Small particles hold more water and nutrients because a gram of clay has an enormous total surface area for water films to cling to, and clay (and humus) particles carry negative charges that attract and hold positively charged nutrient ions (cations). Sandy soils (mostly sand, with little silt and clay) have large pores, drain fastest and are the most permeable, but hold little water or nutrients; clay soils hold the most water and the most nutrients (highest cation exchange capacity, CEC, the ability to hold positively charged nutrient ions such as Ca²⁺, Mg²⁺, K⁺ and NH₄⁺ against leaching) but drain slowly and compact easily; loams balance the two. Waterlogged soil runs out of oxygen, so roots suffocate, denitrification removes nitrogen, and toxic reduced compounds build up. Leaf litter, diverse plant cover and organic matter support rich communities of soil invertebrates, fungi and bacteria. Some wood-decaying fungi even glow (foxfire). Practices that protect soil include conservation tillage (no-till), cover crops, crop rotation, contour plowing, terracing on slopes, windbreaks and adding organic matter. The Dust Bowl of the 1930s showed what happens when deep-rooted prairie grasses are plowed up in a drought-prone region and the soil is left bare. Many U.S. states have an official state soil (Wisconsin's is the Antigo silt loam; Texas's is the Houston Black clay). The scientific study of soils is pedology (and of soils as a medium for crops, edaphology).

Competition in the plant community

Plants compete for light, water and nutrients (and space and pollinators), both with their own species (intraspecific competition) and with others (interspecific competition). Light competition is one-sided: a taller plant shades a shorter one, but not the reverse. Root competition for water and nutrients is more symmetric. In grasslands, plants compete for light by growing tall and slender; in forests, the canopy captures most light. The botanist Augustin Pyramus de Candolle wrote in 1820 that all plants of a region are "at war" with one another, an idea Darwin built on.

• Exploitative vs. interference competition. In exploitative (scramble) competition plants simply use up a shared resource first (roots draining soil water); in interference competition one directly harms or blocks another, as with allelopathy or physical crowding.
• Competitive exclusion and resource partitioning. Two species cannot share exactly the same limiting resources indefinitely (Gause's principle). Coexisting plants partition them (niche partitioning): shade-tolerant species in the understory, deep-rooted species tapping groundwater while shallow roots take rain, and species that grow in different seasons. David Tilman's resource-ratio (R*) theory predicts that, for a single limiting resource, the species able to draw that resource down to the lowest level (lowest R*) wins.
• Allelopathy. Some plants release chemicals (allelochemicals, secondary metabolites) that suppress the germination or growth of neighbors. Black walnut's juglone is the standard example, so gardens near black walnuts struggle (tomatoes are especially sensitive). Others: sunflowers, eucalyptus, tree of heaven, garlic mustard, spotted knapweed, sorghum and rye (whose residues are used as weed-suppressing cover crops in sustainable agriculture).
• Life-history strategies. Fast-growing, short-lived colonizers with high seed output (many annual weeds; ruderals or r-selected species) do well after disturbance; slow-growing, long-lived competitors take over as resources become scarce; stress-tolerators persist where resources are always scarce (Grime's competitor, stress-tolerator and ruderal triangle).
• Succession. Primary succession starts on bare rock or new lava with no soil; lichens (and mosses) are the classic pioneer species, breaking down rock and adding organic matter. Secondary succession follows a disturbance that leaves soil and seed bank intact (fire, an abandoned field, a clear-cut) and proceeds faster, typically annual weeds → perennials and grasses → shrubs → trees, ending in a relatively stable climax community until the next disturbance. After a disturbance, succession does not always rebuild the original community: the new climax can differ in composition if soils, seed sources, climate or invasive species have changed. Diversity usually rises quickly in early succession and then levels off or even declines (the rate of change decelerates) as dominant competitors take over. Connell and Slatyer (1977) described three ways early species affect later ones: facilitation (they make the site better, as nitrogen-fixing alders do for spruce after glaciers retreat), tolerance (later species are simply better competitors under low resources) and inhibition (early species hold the site until they die or are disturbed).
• Fire. In fire-adapted ecosystems (chaparral, prairies, longleaf pine savanna) fire recycles nutrients, clears competitors and triggers seeds. Chaparral recovers by secondary succession: shrubs resprout from root crowns and burls (lignotubers, woody swellings at the base packed with dormant buds) and fire-cued seeds germinate, with grasses and annual herbs first. Wildfires are classed as ground fires (smoldering through peat and deep organic soil), surface fires (burning litter, grasses and shrubs; the type most fire-adapted forests are built to survive) and crown fires (racing through the treetops, the most destructive). Prescribed (controlled) burns reduce fuel buildup and maintain these communities; decades of fire suppression let dead fuel accumulate, which feeds catastrophic wildfires and favors some pathogens.

Plant-animal and plant-microbe interactions

Mycorrhizae ("fungus roots") are found in roughly 80 to 90% of land plant species. Arbuscular mycorrhizae (endomycorrhizae, also called vesicular-arbuscular mycorrhizae or VAM, after the arbuscules and the storage vesicles many form inside roots; fungi of the Glomeromycota) push branched arbuscules inside root cortex cells and are the most common type, including most crops; they cannot complete their life cycle without a host (obligate symbionts). Ectomycorrhizae wrap roots in a fungal sheath and grow between cortex cells (the Hartig net) on pines, oaks, birches and beeches. Orchids and heaths have their own types. The fungus extends the root's reach for phosphorus, water and other nutrients in exchange for up to about a fifth of the plant's sugar, and mycorrhizae helped the first plants colonize land.

Plant defenses against herbivores are physical (thorns, spines, prickles, trichomes, tough leaves, silica in grasses, waxes) and chemical (secondary metabolites: alkaloids such as nicotine, caffeine and solanine, benzoxazinoids such as DIMBOA in young corn, wheat and rye, which deter insects and fungi, tannins that bind proteins and make tissue hard to digest, terpenoids, cyanogenic glycosides, glucosinolates in mustards, latex). Many defenses are induced: chewing triggers jasmonate signaling, protease inhibitors and volatile compounds that attract predators and parasitoid wasps of the herbivore. Plants put the most defense into their most valuable and vulnerable tissues: tannins are concentrated in oak acorns, and caffeine in coffee and tea leaves and seeds acts as a natural insecticide. Even nectar can carry small doses of alkaloids such as nicotine and caffeine, which deter nectar robbers and, in caffeine's case, help bees remember the flower. Specialist herbivores turn defenses into an advantage: monarch caterpillars feed only on milkweed and store its toxic cardiac glycosides, which protect them from birds.

Adaptations to environment

Carnivorous plants trap prey five ways: pitfall traps (pitcher plants, Sarracenia and Nepenthes), snap traps (Venus flytrap, Dionaea, closing when trigger hairs are touched twice), flypaper traps of sticky glandular hairs (sundews, Drosera; butterworts), suction bladders (bladderworts, Utricularia) and lobster-pot traps (Genlisea). They still photosynthesize; insects supply nutrients, not energy.

Raunkiær's life forms classify plants by where their renewal buds survive the unfavorable season: phanerophytes (buds well above ground: trees and shrubs, dominant in the tropics), chamaephytes (buds just above the soil, under snow: low shrubs, cushion plants), hemicryptophytes (buds at the soil surface: many grassland perennials), cryptophytes or geophytes (buds underground on bulbs, rhizomes and tubers, or under water) and therophytes (survive only as seeds: annuals, dominant in deserts). The harsher the climate, the better protected the buds.

Desert flora to know: cacti (Cactaceae, recognized by areoles), agaves and yuccas, creosote bush and puncturevine (Zygophyllaceae), mesquite (Fabaceae), ocotillo and Welwitschia. Famous aquatic plants: eelgrass (Zostera marina), the main seagrass of Chesapeake Bay and a nursery for blue crabs, is a flowering plant (a monocot), not an alga; seagrass meadows such as those of Posidonia oceanica in the Mediterranean are clonal and are estimated to be many thousands of years old, among the oldest living organisms. Periphyton is the community of algae, cyanobacteria and microbes attached to submerged surfaces (rocks, plants) in streams, lakes and wetlands.

Not every non-native plant is invasive (most garden plants never escape). Invasive species are non-native species that spread from where they were introduced and harm ecosystems, economies or health. They typically grow fast, reproduce heavily or vegetatively, tolerate many conditions and arrived without their natural enemies, so they outcompete natives, alter food webs and habitats and reduce biodiversity. Plant examples: Chinese wisteria (brought from Asia in the 1800s as a porch vine), kudzu, purple loosestrife, Japanese knotweed, garlic mustard, English ivy, tree of heaven, water hyacinth (Eichhornia crassipes), hydrilla, Japanese honeysuckle, multiflora rose, buckthorn, Callery (Bradford) pear, cheatgrass (which fuels more frequent fires) and, in some regions, butterfly bush. Homeowners should remove invasive plants and dispose of them so seeds and fragments cannot spread (bagging, not composting); land managers add biological control, such as leaf beetles released against purple loosestrife. Native species such as red maple are not invasive in their native range.

Plants, food and people

Use of plant materials by animals and humans

Most animals cannot make enzymes that break down cellulose, the most abundant organic compound on land. Herbivores rely on microbes: ruminants (cows, sheep, deer) ferment plants in the rumen and rechew the cud; hindgut fermenters (horses, rabbits) ferment in the cecum and colon; termites carry gut symbionts (and also make some cellulase of their own). Some herbivores specialize on one plant despite its toxins: koalas eat almost nothing but eucalyptus leaves, and giant pandas eat bamboo. Humans get almost no energy from cellulose; to us it is dietary fiber.

People use plants for food, fiber, wood and paper, fuel, rubber, cork, dyes, beverages, spices and medicines. Plants give us structural materials because their cell walls are built of cellulose and lignin.

Fibers come from four places, and all are mostly cellulose:

Bast fibers are freed by retting: soaking or dew-wetting the stems so microbes rot away the pectin that glues fibers to the surrounding tissue (flax, hemp, jute, kenaf, ramie). U.S. paper money is not paper from wood pulp but a blend of about 75% cotton and 25% linen.

Wood is secondary xylem. Hardwood comes from angiosperm trees (oak, maple, walnut) and contains vessels and fibers; softwood comes from conifers (pine, spruce, fir) and is mostly tracheids. Paper is made from cellulose fibers of wood pulp after most of the lignin is removed. Wood's specific gravity is its density divided by the density of water (oven-dry mass divided by the mass of an equal volume of water); denser wood is generally stronger in tension and compression, and wood's specific gravity rises as it dries and shrinks. Tannins from oak and other barks are used to tan animal hides into leather. Other plant products: rubber from the latex of Hevea brasiliensis, cork from the cork cambium of the cork oak, turpentine and rosin from pine resin, dyes such as indigo and henna, and biofuels: ethanol fermented from corn and sugarcane, biodiesel made from the oils of soybean, rapeseed (canola), oil palm and the shrub Jatropha curcas, and cellulosic ethanol from grasses such as switchgrass.

Spices, beverages and flavorings come from every plant organ:

Production of foodstuffs and plant products

A handful of grasses feed the world: rice, wheat and maize supply a large share of human food energy (often quoted at around half). Other staples include potatoes, cassava, soybeans, sorghum and millets. Soybeans are the richest pulse in protein (roughly 35 to 40% of dry weight, versus about 20 to 27% for peas, beans, lentils, black gram and pigeon pea) and also yield oil, which is why they are the world's leading oilseed and a major feed crop. Crops were domesticated independently in several centers of origin (Vavilov's idea): the Fertile Crescent of the Middle East (wheat, barley, peas, lentils, about 10,000 years ago), China (rice, soybeans), Mesoamerica (maize from the wild grass teosinte, beans, squash, chili peppers, cacao), the Andes (potatoes, quinoa), Africa (sorghum, coffee from Ethiopia) and New Guinea and Southeast Asia (sugarcane, bananas). Domestication is artificial selection: people, not nature, chose which plants reproduced, unlike natural selection, which favors whatever survives and reproduces best in the wild. Domestication selected for seeds that do not shatter off the plant, larger fruits and seeds, and seeds that germinate together without dormancy. In the United States, California grows far more fruits, nuts and vegetables than any other state (most of the nation's almonds, grapes, lettuce, tomatoes for processing, strawberries and broccoli), Florida grows much of the winter fresh-vegetable supply and, with California, most of the oranges (citrus greening has sharply cut Florida's crop), the Corn Belt (Iowa, Illinois, Nebraska) leads corn and soybeans, Kansas and North Dakota lead wheat, Idaho leads potatoes, Washington leads apples, Texas leads cotton and Georgia leads peanuts. Shifting cultivation (slash-and-burn, swidden) clears and burns a forest patch, farms it for a few years until fertility drops and weeds build up, then moves to new land and lets the old plot regrow.

The Netherlands dominates the world cut-flower trade (roughly half of global exports, much of it through its flower auctions), followed by growers in Colombia, Ecuador and Kenya. Converting raw produce into canned, frozen, dried or milled products is called processing, and buying locally grown food mainly cuts the fuel used to transport it. Milled white rice is a poor source of vitamins (the bran and germ that carry B vitamins are removed, and rice grains have no vitamin A at all), one reason vitamin-fortified rice and beta-carotene-rich Golden Rice were developed. Processing turns raw crops into foods: milling separates bran and germ from the endosperm (white flour); fermentation by yeast makes bread rise and turns sugars into alcohol; malting lets germinating barley convert its starch to sugar (gibberellin triggers the enzymes); bacteria ferment cabbage into sauerkraut. Food safety includes plant toxins: potatoes exposed to light turn green (chlorophyll) and at the same time build up the bitter glycoalkaloid solanine, concentrated in green skin and sprouts, so green or sprouting parts should be cut away or the potato discarded. Solanine and related alkaloids occur across the nightshade family (potatoes, tomatoes, eggplants), not in onions. Soybeans become soy milk (soaked, ground and strained beans), tofu (soy milk curdled with a calcium or magnesium salt and pressed), tempeh (whole soybeans fermented by a Rhizopus mold), miso and soy sauce (fermented with Aspergillus mold) and edamame (immature green pods). Corn is most sensitive to drought at tasseling and silking (pollination), then during grain fill; water stress then cuts kernel number and yield far more than stress during vegetative growth.

The Green Revolution (1950s-1970s) raised yields with semi-dwarf wheat and rice, synthetic fertilizer, irrigation and pesticides, led by Norman Borlaug in Mexico and spreading to India and Pakistan. The dwarfing genes alter gibberellin production or response, giving short, sturdy stems that hold heavy heads of grain without falling over (lodging). It averted famines and kept food prices low, but it also increased fertilizer runoff and pesticide use, depleted groundwater, encouraged monocultures of a few varieties (more, not less, monoculture), displaced traditional landraces, and favored farmers who could afford the inputs. The Haber-Bosch process that supplies its nitrogen fertilizer is a major source of nitrogen pollution. Water limits agriculture in dry regions such as California, where water-hungry tree crops like almonds and pistachios are under scrutiny.

Crops and garden plants A to Z

Use this table to answer the "which part do we eat", "how is it propagated", "cool or warm season" and "what is its signature disease" questions that make up much of a horticulture or human-uses section. Each row is one crop or garden plant, sorted alphabetically by common name, so you can scan a single column (for example every stem tuber, every dioecious crop or every CAM plant) to catch a whole category at once. Fruit and organ names follow the Fruits and seeds and the Roots, stems and leaves sections of this guide.

ReferenceCrops and garden plants A-Z· 229 rows

"Grown as annual" means botanically biennial or perennial but harvested in one season. SD, LD, DN = short-day, long-day, day-neutral. C3, C4, CAM = photosynthetic pathway (noted only where tests ask). "Chilling" = hours near 32 to 45 °F needed to break bud dormancy. "Pollinizer" = a second, compatible cultivar planted for cross-pollination.

229 rows

Plant (scientific name)	Family	Habit and life cycle	Part used (botanical term)	Propagation	Season and culture	Main pests and diseases	Notes
African violet (Saintpaulia ionantha, now Streptocarpus)	Gesneriaceae	Herbaceous rosette; perennial houseplant	Ornamental (flowers, foliage)	Leaf-petiole cuttings; division; seed	Bright indirect light; room-temperature water (cold water spots leaves); water from below	Mealybugs; cyclamen mites; crown and root rot	Native to Tanzania and Kenya; fuzzy leaves
Agave, blue (Agave tequilana)	Asparagaceae	Succulent rosette, monocot; monocarpic perennial	"Piña" (stem core with leaf bases), roasted for tequila	Offsets (hijuelos), so fields are clonal	Hot, dry; about 6 to 8 years (range 5 to 12) to maturity before harvest	Agave snout weevil; Fusarium	CAM; bat-pollinated if allowed to flower; low genetic diversity from clonal planting; stores fructans (agavins), which are hydrolyzed to make fructose-rich agave syrup
Alfalfa (Medicago sativa)	Fabaceae	Herbaceous perennial with deep taproot	Forage (leaves and stems, hay)	Seed (inoculated with Sinorhizobium meliloti)	Cool-season; needs pH about 6.5 or higher and good drainage; cut several times a year	Alfalfa weevil; potato leafhopper; root rots	N-fixing legume; "queen of forages"; C3
Almond (Prunus dulcis)	Rosaceae	Deciduous tree; perennial	Seed of a drupe (hull = dried exocarp and mesocarp; shell = endocarp)	Budded onto peach or peach-almond hybrid rootstock	Mediterranean climate; blooms very early (frost risk); most cultivars self-incompatible, need pollinizer rows and honeybees	Navel orangeworm; hull rot; brown rot	California grows about 80% of world supply; bitter almonds contain amygdalin (cyanogenic)
Aloe (Aloe vera)	Asphodelaceae	Succulent monocot rosette; perennial	Leaf gel (water-storage parenchyma)	Offsets (pups)	Full sun to bright light; frost-tender; let soil dry	Root rot from overwatering; mealybugs	CAM; latex under the leaf skin is a laxative (aloin)
Amaryllis (Hippeastrum hybrids)	Amaryllidaceae	Monocot bulb; perennial	Ornamental (flowers)	Offset bulbs; seed; bulb cutting (twin-scaling)	Forced indoors for winter bloom; outdoors only about zones 8 to 10	Red blotch (Stagonospora); bulb mites; narcissus bulb fly	South American; true Amaryllis belladonna is South African; bulbs toxic
Apple (Malus domestica)	Rosaceae	Deciduous tree; perennial	Fruit (pome; flesh is hypanthium)	Budding or grafting onto clonal rootstocks (Malling 'M.9' dwarfing, 'M.7', 'MM.111'); seeds do not come true	Temperate, about zones 3 to 8; needs chilling; most need a pollinizer (another cultivar or crabapple) and bees; harvest late summer to fall	Codling moth; apple scab (Venturia inaequalis); fire blight (Erwinia amylovora); cedar-apple rust	Climacteric; origin Central Asia (wild Malus sieversii, Kazakhstan); Washington leads U.S.
Apricot (Prunus armeniaca)	Rosaceae	Deciduous tree; perennial	Fruit (drupe)	Budded onto apricot, peach or plum rootstock	Blooms very early, so late frosts kill crops; most cultivars self-fruitful	Brown rot; bacterial canker; plum curculio	Origin Central Asia and China
Artichoke, globe (Cynara cardunculus var. scolymus)	Asteraceae	Herbaceous perennial (some grown as annual)	Immature inflorescence (head): fleshy bract bases and receptacle ("heart")	Rooted offshoots, division; seed for annual types	Mild, cool, foggy coast (Castroville, California); hardy only in mild winters	Aphids; slugs and snails; artichoke plume moth	Thistle relative; Mediterranean origin; the "choke" is immature florets
Arugula (Eruca vesicaria)	Brassicaceae	Herbaceous; cool-season annual	Leaves	Seed, direct-sown	Cool; bolts in heat and long days	Flea beetles	Peppery from glucosinolates; Mediterranean
Ash (Fraxinus americana, F. pennsylvanica)	Oleaceae	Deciduous tree; perennial	Timber (bats, tool handles); shade tree	Seed	Full sun; widely planted street tree	Emerald ash borer (Agrilus planipennis, found in Michigan 2002)	Opposite pinnately compound leaves; single samaras; mostly dioecious
Asparagus (Asparagus officinalis)	Asparagaceae	Herbaceous perennial monocot	Young shoots (spears = stems); the ferny "leaves" are cladophylls	One-year crowns set in trenches; seed	Cool-season perennial; harvest spring starting the 2nd or 3rd year for 6 to 8 weeks; tolerates salt; pH about 6.5 to 7.5	Asparagus beetle; Fusarium crown rot; asparagus rust	Dioecious; all-male hybrids (Jersey series) yield more; beds last 15 to 20+ years
Avocado (Persea americana)	Lauraceae	Evergreen tree; perennial	Fruit (one-seeded berry)	Grafted onto seedling or clonal rootstocks (chosen for Phytophthora tolerance)	Subtropical, frost-tender; perfect drainage; flowers type A or B (each opens female, then male, at different times), so A and B cultivars interplanted	Phytophthora cinnamomi root rot; thrips	Climacteric; ripens only after picking; 'Hass' is type A; origin Mexico and Central America; persin toxic to birds and livestock
Azalea and rhododendron (Rhododendron spp.)	Ericaceae	Woody shrub (evergreen or deciduous); perennial	Ornamental (flowers)	Cuttings; layering	Acid soil (pH about 4.5 to 6); part shade; shallow roots, mulch; iron chlorosis in alkaline soil	Phytophthora root rot; azalea lace bug; leaf gall (Exobasidium)	Toxic (grayanotoxins; "mad honey"); ericoid mycorrhizae
Bamboo (Phyllostachys, Bambusa and others)	Poaceae	Woody grass; perennial	Culms (stems) for building; young shoots eaten	Rhizome division	Running types (leptomorph rhizomes) spread aggressively; clumping types (pachymorph) do not	Bamboo mites; few serious pests	Among the fastest-growing plants; many species flower all at once at long intervals, then die (monocarpic)
Banana (Musa acuminata × M. balbisiana cultivars)	Musaceae	Giant herb (pseudostem of rolled leaf sheaths); perennial monocot	Fruit (berry), parthenocarpic	Suckers (pups) from the underground rhizome (corm); tissue culture	Tropical, frost-free; rich moist soil; each pseudostem fruits once	Panama disease (Fusarium wilt, TR4); black Sigatoka; banana bunchy top virus	Seedless sterile triploids ('Cavendish', AAA); 'Gros Michel' was lost to Panama disease; origin Southeast Asia; not a tree
Barberry, common (Berberis vulgaris)	Berberidaceae	Deciduous spiny shrub; perennial	Ornamental, hedges	Seed; cuttings	Hardy; sun to part shade	Alternate host of wheat stem rust	U.S. eradication campaign from 1918 to break the stem rust cycle; spines are modified leaves; Japanese barberry (B. thunbergii) is an invasive escape
Barley (Hordeum vulgare)	Poaceae	Grass; cool-season annual (winter and spring types)	Grain (caryopsis, usually hulled)	Seed (drilled)	Cool, dry; most salt- and drought-tolerant small grain; short season	Powdery mildew; barley yellow dwarf virus (aphids); Fusarium head blight	C3; LD; self-pollinated; malting (germinated grain makes amylases) for beer; Fertile Crescent founder crop
Basil (Ocimum basilicum)	Lamiaceae	Herbaceous; warm-season annual	Leaves	Seed; stem cuttings root readily in water	Frost-tender; full sun, warm soil; pinch flowers to keep leafy	Basil downy mildew (Peronospora belbahrii); Fusarium wilt	Square stems, opposite aromatic leaves; origin India
Bean, common (snap, dry) (Phaseolus vulgaris)	Fabaceae	Herbaceous; warm-season annual, bush or pole (twining vine)	Immature pods (legume) for snap beans; seeds for dry beans (kidney, pinto, navy, black)	Seed, direct-sown about 1 in. deep after frost in soil 60 °F or warmer	Frost-tender; full sun (6 to 8+ hr); self-pollinating; pick snap beans young	Mexican bean beetle; bean common mosaic virus; anthracnose; white mold	Epigeal germination; N-fixing (Rhizobium); one of the Three Sisters; raw kidney beans contain toxic lectin (phytohaemagglutinin); origin Mesoamerica and Andes
Beet (Beta vulgaris, Conditiva group)	Amaranthaceae	Herbaceous; biennial grown as cool-season annual	Storage root (swollen taproot plus hypocotyl); leaves (greens)	Seed; each "seed" is a fruit cluster holding several seeds, so thin seedlings	Cool-season, frost-tolerant; spring or fall	Cercospora leaf spot; leaf miners; boron deficiency (internal black spot)	Red betalain pigments (betanin), not anthocyanins; rings from extra cambia; chard and sugar beet are the same species
Begonia (Begonia spp.)	Begoniaceae	Herbaceous perennial (wax begonia grown as annual; tuberous and rex types)	Ornamental (flowers, foliage)	Stem cuttings; leaf cuttings (rex); tubers; dust-fine seed	Shade to part shade; frost-tender	Powdery mildew; botrytis; root rot	Monoecious, separate male and female flowers on one plant
Bermudagrass (Cynodon dactylon)	Poaceae	Turf grass; warm-season perennial	Leaves (lawn, sports turf, forage)	Sprigs, plugs and sod (stolons and rhizomes); seed for common types	Full sun only; drought-tolerant; goes brown and dormant after frost	Spring dead spot; armyworms; mole crickets	C4; aggressive garden weed; origin Africa
Black pepper (Piper nigrum)	Piperaceae	Woody climbing vine; perennial	Fruit (small drupe, "peppercorn")	Stem cuttings	Humid tropics; needs support posts or trees and partial shade	Phytophthora foot rot ("quick wilt")	Black = unripe fruit dried; white = ripe fruit with pericarp removed; piperine; origin Western Ghats, India
Blackberry (Rubus spp.)	Rosaceae	Woody perennial crown with biennial canes (primocane, floricane)	Aggregate fruit of drupelets; core (receptacle) comes off with the fruit	Tip layering; root cuttings; suckers	Self-fruitful; full sun; trellis trailing types; remove floricanes after they fruit	Orange rust; anthracnose; spotted wing drosophila	Raspberry differs: its fruit pulls off the receptacle, leaving a hollow
Black-eyed Susan (Rudbeckia hirta)	Asteraceae	Herbaceous; biennial or short-lived perennial	Ornamental (flower heads)	Seed (self-sows); division	Full sun; drought-tolerant; summer to fall bloom	Powdery mildew; Septoria leaf spot	Native prairie wildflower; Maryland state flower; head of yellow ray florets and dark disk florets
Blueberry, highbush (Vaccinium corymbosum)	Ericaceae	Deciduous woody shrub; perennial	Fruit (berry from an inferior ovary)	Softwood or hardwood cuttings; tissue culture	Acid soil pH about 4.5 to 5.5, high organic matter; needs chilling (rabbiteye and southern highbush need less); plant 2+ cultivars for better set; bee (buzz) pollination; harvest midsummer	Mummy berry; spotted wing drosophila; birds; iron chlorosis in high-pH soil	Native to North America; ericoid mycorrhizae, few root hairs; ripening is atypical climacteric (classification debated)
Bluebonnet, Texas (Lupinus texensis)	Fabaceae	Herbaceous; winter annual	Ornamental (wildflower)	Seed (hard coat, scarify)	Fall-sown, blooms in spring; full sun, well-drained, alkaline-tolerant	Root rot in wet soil	Texas state flower; N-fixing legume; seeds toxic
Boston fern (Nephrolepis exaltata 'Bostoniensis')	Nephrolepidaceae	Fern; perennial houseplant	Ornamental (fronds)	Division; plantlets on runners (stolons); no seeds (spores, but the cultivar is propagated vegetatively)	Bright indirect light; high humidity; keep evenly moist	Mealybugs; scale; leaf drop in dry air	Non-flowering vascular plant
Boxwood (Buxus sempervirens and others)	Buxaceae	Evergreen shrub; perennial	Ornamental (hedges, topiary)	Cuttings	Sun to part shade; well-drained soil	Boxwood blight (Calonectria pseudonaviculata); boxwood leafminer	Toxic alkaloids, so deer-resistant
Brazil nut (Bertholletia excelsa)	Lecythidaceae	Giant emergent rainforest tree; perennial	Seed (10 to 25 in a woody capsule)	Seed; mostly wild-harvested	Amazon rainforest; plantations yield poorly	Few pests	Pollinated by large bees (euglossine and others); agoutis gnaw open the pods and disperse seeds; Bolivia is the top exporter; seeds high in selenium
Broccoli (Brassica oleracea, Italica group)	Brassicaceae	Herbaceous; biennial species grown as cool-season annual	Immature inflorescence (flower buds and stalks)	Seed; transplants	Cool-season, frost-tolerant; harvest before yellow petals show; side shoots follow the main head	Imported cabbageworm; cabbage looper; aphids; clubroot (Plasmodiophora brassicae)	Boron deficiency causes hollow stem; cabbage, kale, collards, kohlrabi, cauliflower and Brussels sprouts are all B. oleracea (wild cabbage, Mediterranean)
Brussels sprouts (Brassica oleracea, Gemmifera group)	Brassicaceae	Herbaceous; biennial grown as annual	Enlarged axillary buds	Seed; transplants	Long, cool season; flavor improves after frost; harvest from the bottom up	Cabbageworms; aphids; clubroot	Glucosinolates give the bitterness
Buckwheat (Fagopyrum esculentum)	Polygonaceae	Herbaceous; warm-season annual	Fruit (achene, triangular), milled as a pseudocereal	Seed	Short season (about 10 to 12 weeks); frost-tender; grows on poor soil	Few pests	Not a grass; gluten-free; smother cover crop and bee plant; heterostylous (pin and thrum flowers) so insects needed
Cabbage (Brassica oleracea, Capitata group)	Brassicaceae	Herbaceous; biennial grown as cool-season annual	Head = large terminal bud of overlapping leaves	Seed; transplants	Cool-season, frost-tolerant; heads split after heavy water uptake; needs vernalization to flower	Imported cabbageworm; cabbage looper; black rot (Xanthomonas campestris); clubroot	Sauerkraut and kimchi (Napa cabbage is B. rapa)
Cacao (Theobroma cacao)	Malvaceae	Evergreen understory tree; perennial	Seeds ("beans") from a large pod; fermented, dried, roasted	Seed; grafting; cuttings	Humid tropics within about 20° of the equator; shade; flowers borne on trunk (cauliflory)	Black pod (Phytophthora); witches' broom; frosty pod; cocoa swollen shoot virus	Pollinated by tiny midges; theobromine and caffeine; origin upper Amazon; Ivory Coast is the top producer
Calla lily (Zantedeschia aethiopica)	Araceae	Herbaceous monocot; perennial from a rhizome	Ornamental (cut flower)	Division of rhizomes	Tender (outdoors about zones 8 to 10); moist soil	Bacterial soft rot (Pectobacterium); aphids	White "flower" is a spathe around a spadix; not a true lily; calcium oxalate, toxic; South Africa
Camellia (Camellia japonica, C. sasanqua)	Theaceae	Evergreen shrub; perennial	Ornamental (flowers in fall to spring)	Cuttings; grafting; layering	Acid soil; part shade; mild winters	Tea scale; camellia petal blight	Same genus as tea
Canna (Canna × generalis)	Cannaceae	Herbaceous monocot; perennial from a rhizome	Ornamental (flowers, foliage)	Division of rhizomes	Hot sun, moist soil; tender, dig rhizomes in the North	Canna leaf roller; canna rust; canna viruses	Showy "petals" are petaloid staminodes; hard round seeds ("Indian shot")
Canola (rapeseed) (Brassica napus)	Brassicaceae	Herbaceous; cool-season annual (winter and spring types)	Seeds (from a silique), pressed for oil	Seed	Cool, temperate; Canada a top producer	Flea beetles; blackleg; Sclerotinia stem rot	"Canola" = rapeseed bred in Canada (1970s) for low erucic acid and low glucosinolates; most North American canola is herbicide-tolerant (largely GM); B. napus is the amphidiploid of B. rapa × B. oleracea (triangle of U)
Cantaloupe (muskmelon) (Cucumis melo)	Cucurbitaceae	Herbaceous vine; warm-season annual	Fruit (pepo)	Seed or transplants after frost	Warm, full sun; bees needed; harvest at "full slip" (stem separates easily)	Cucumber beetles (bacterial wilt); powdery mildew; aphids	Sugar does not rise after harvest; U.S. "cantaloupe" is netted muskmelon (var. reticulatus); origin Africa or Asia
Cardamom (Elettaria cardamomum)	Zingiberaceae	Herbaceous monocot; perennial from a rhizome	Seeds in a dried capsule	Rhizome division; seed	Shaded humid tropical forest	Thrips; viral and rot diseases	Among the costliest spices (after saffron and vanilla); native to the Western Ghats of India; Guatemala and India are the top producers (Guatemala leads exports)
Carnation (Dianthus caryophyllus)	Caryophyllaceae	Herbaceous perennial	Ornamental (cut flower)	Stem cuttings	Cool, bright greenhouses; full sun	Fusarium wilt; thrips; aphids	Very sensitive to ethylene ("sleepiness"); long vase life; Colombia supplies most U.S. imports
Carrot (Daucus carota subsp. sativus)	Apiaceae	Herbaceous; biennial grown as cool-season annual	Storage taproot (mostly secondary phloem and xylem)	Seed only, direct-sown (slow to germinate; do not transplant)	Cool-season, frost-tolerant; deep, loose, stone-free soil (rocks and clods cause forking); hill to prevent green shoulders	Carrot rust fly; aster yellows (phytoplasma, leafhoppers); Alternaria leaf blight	Orange beta-carotene types developed in the Netherlands about the 1600s; wild form is Queen Anne's lace; fruit a schizocarp; needs vernalization to flower
Cashew (Anacardium occidentale)	Anacardiaceae	Evergreen tropical tree; perennial	Seed inside the kidney-shaped nut (drupe), which hangs below the swollen pedicel (cashew apple, an accessory fruit)	Seed; grafting	Tropical lowlands; drought-tolerant	Tea mosquito bug; anthracnose	Shell oil (anacardic acid, cardol) is caustic like poison ivy, so cashews are never sold in the shell; origin northeastern Brazil
Cassava (Manihot esculenta)	Euphorbiaceae	Woody shrub; perennial grown as annual	Storage (tuberous) roots	Stem cuttings	Tropical; tolerates drought and poor, acid soils; harvest 8 to 24 months	Cassava mosaic disease (whiteflies); cassava brown streak	Cyanogenic glucosides (linamarin) must be removed by soaking, grating, cooking; tapioca; staple for hundreds of millions; origin Amazon basin, Brazil
Castor bean (Ricinus communis)	Euphorbiaceae	Shrub or small tree; perennial, grown as warm-season annual ornamental	Seed (castor oil, ricinoleic acid)	Seed	Hot sun; frost-tender	Few pests	Seed contains ricin, one of the most toxic plant proteins (the refined oil is safe); seed has a caruncle; albuminous seed; monoecious; origin East Africa
Cauliflower (Brassica oleracea, Botrytis group)	Brassicaceae	Herbaceous; biennial grown as cool-season annual	"Curd" = proliferated inflorescence meristems (immature flower stalks)	Seed; transplants	Cool, steady conditions; blanch by tying leaves over the curd; stress causes "buttoning"	Cabbageworms; clubroot; boron deficiency (brown curd, hollow stem)	Molybdenum deficiency causes whiptail
Celery (Apium graveolens var. dulce)	Apiaceae	Herbaceous; biennial grown as annual	Petioles (leaf stalks; collenchyma "strings")	Seed (tiny, slow, needs light); transplants	Long, cool season; heavy water and fertility; blanching; long cold spells cause bolting	Early and late blights (Cercospora, Septoria); aster yellows	Calcium deficiency causes blackheart; boron deficiency cracked stem; psoralens can cause skin photosensitivity
Chard, Swiss (Beta vulgaris, Cicla group)	Amaranthaceae	Herbaceous; biennial grown as annual	Leaves and thick petioles	Seed (seed clusters, thin seedlings)	Cool-season but heat-tolerant; cut-and-come-again	Leaf miners; Cercospora leaf spot	Same species as beet and sugar beet
Cherry, sour (tart) (Prunus cerasus)	Rosaceae	Deciduous tree; perennial	Fruit (drupe)	Budded onto Mahaleb or Mazzard rootstock	Hardy; needs chilling; self-fruitful ('Montmorency')	Cherry leaf spot (Blumeriella jaapii); brown rot; cherry fruit fly	Michigan leads U.S. production
Cherry, sweet (Prunus avium)	Rosaceae	Deciduous tree; perennial	Fruit (drupe)	Budded onto Mazzard, Mahaleb or dwarfing 'Gisela' rootstocks	Needs chilling; most need a pollinizer ('Stella', 'Lapins' self-fruitful); rain at ripening cracks fruit	Bacterial canker; brown rot; spotted wing drosophila; birds	'Bing'; Washington leads U.S. production; non-climacteric
Chestnut (Castanea dentata, American; C. mollissima, Chinese)	Fagaceae	Deciduous tree; perennial	Nut in a spiny bur (cupule)	Seed; grafting	Acid, well-drained soil; needs cross-pollination	Chestnut blight (Cryphonectria parasitica, from Asia, early 1900s)	Blight killed about 4 billion American chestnuts; resistant Chinese chestnut grown for nuts; blight-tolerant hybrid and transgenic lines in development; monoecious catkins
Chickpea (garbanzo) (Cicer arietinum)	Fabaceae	Herbaceous; cool-season annual	Seeds (pulse)	Seed	Drought-tolerant; dryland, semi-arid	Ascochyta blight; Fusarium wilt	Self-pollinated; hummus; desi (small, dark) and kabuli (large, cream) types; Fertile Crescent founder crop; India the top producer
Chicory and Belgian endive (Cichorium intybus)	Asteraceae	Herbaceous perennial (biennial in culture)	Leaves; blanched forced shoots ("chicons"); roasted taproot (coffee substitute, inulin)	Seed; roots dug and forced in the dark	Cool-season; roots forced indoors in darkness for endive	Few pests; slugs	Classic example of blanching (excluding light to keep tissue pale and less bitter); blue roadside wildflower
Chives (Allium schoenoprasum)	Amaryllidaceae	Herbaceous monocot; perennial from small bulbs	Leaves (hollow); edible flowers	Division of clumps; seed	Cold-hardy; sun to part shade	Onion thrips	Lilac-pink flower heads (umbels)
Christmas cactus (Schlumbergera × buckleyi)	Cactaceae	Epiphytic succulent; perennial houseplant	Ornamental (flowers)	Stem-segment cuttings	SD plus cool nights (about 55 to 65 °F) set flower buds; bright indirect light	Root rot from overwatering; bud drop	Flat stem segments are phylloclades (no true leaves); CAM; native to coastal mountains of Brazil
Chrysanthemum (Chrysanthemum × morifolium)	Asteraceae	Herbaceous perennial (garden mums) and greenhouse crop	Ornamental (flower heads, cut and potted)	Stem cuttings; division	SD (fall bloom); greenhouses use blackout cloth or night lighting for year-round crops; pinch for bushiness, disbud for large blooms	Aphids; thrips; chrysanthemum white rust (Puccinia horiana)	Origin China; pyrethrum insecticide comes from the related Tanacetum cinerariifolium
Cilantro (coriander) (Coriandrum sativum)	Apiaceae	Herbaceous; cool-season annual	Leaves (cilantro); fruit, a schizocarp ("coriander seed")	Seed, direct-sown	Cool; bolts fast in heat and long days, so sow in succession	Aphids; powdery mildew	Soapy taste to some people is genetic; umbel flowers
Cinchona (Cinchona spp.)	Rubiaceae	Evergreen tree; perennial	Bark (quinine)	Seed; cuttings	Cool, moist Andean slopes; tropical highlands	Root rots	Quinine was the first effective malaria treatment and flavors tonic water; "Jesuit's bark"; native to the Andes (Peru, Ecuador); national tree of Peru
Cinnamon (Cinnamomum verum)	Lauraceae	Evergreen tree, coppiced as a shrub; perennial	Inner bark (dried into quills)	Seed; cuttings; coppicing	Hot, humid tropics	Leaf spot; stripe canker	True cinnamon from Sri Lanka; cassia (C. cassia) is the common U.S. cinnamon and is higher in coumarin
Clematis (Clematis spp.)	Ranunculaceae	Woody (some herbaceous) climbing vine; perennial	Ornamental (flowers)	Layering; cuttings	"Head in the sun, feet in the shade"; climbs by twining petioles; pruning group depends on bloom time	Clematis wilt; slugs	Showy parts are sepals; fruit an achene with a feathery style; toxic (protoanemonin)
Clove (Syzygium aromaticum)	Myrtaceae	Evergreen tree; perennial	Dried unopened flower buds	Seed	Humid tropics	Sudden death disease; few pests	Eugenol (dental anesthetic); native to the Maluku (Spice) Islands, Indonesia
Clover, white and red (Trifolium repens, T. pratense)	Fabaceae	Herbaceous perennial (white); short-lived perennial (red)	Forage, cover crop, lawn mixes	Seed (inoculated); white clover spreads by stolons	Cool-season legume; tolerates mowing	Clover root borer; root rots	N-fixing (Rhizobium leguminosarum bv. trifolii); red clover is Vermont's state flower; white clover has cyanogenic forms
Coconut (Cocos nucifera)	Arecaceae	Palm (monocot tree); perennial	Fibrous drupe: husk = coir (mesocarp); shell = endocarp; meat = cellular endosperm; water = liquid (free-nuclear) endosperm	Seed (whole nut)	Tropical coasts; salt-tolerant; disperses by floating	Lethal yellowing (phytoplasma); coconut rhinoceros beetle	Copra (dried meat) yields coconut oil; "tree of life"
Coffee (Coffea arabica; C. canephora robusta)	Rubiaceae	Evergreen shrub or small tree; perennial	Seeds ("beans"), two per red drupe ("cherry")	Seed; cuttings; grafting	Arabica: tropical highlands, partial shade, self-fertile; robusta: lowland, self-incompatible, more caffeine	Coffee leaf rust (Hemileia vastatrix); coffee berry borer	Arabica origin Ethiopia; Brazil is the top producer; caffeine deters insects and is allelopathic
Coleus (Coleus scutellarioides)	Lamiaceae	Herbaceous tender perennial grown as annual	Ornamental (colorful foliage)	Stem cuttings (root easily); seed	Shade and sun types; frost-tender; pinch flower spikes	Mealybugs; downy mildew	Square stem, opposite leaves; formerly Solenostemon
Coneflower, purple (Echinacea purpurea)	Asteraceae	Herbaceous perennial	Ornamental; roots and tops as herbal medicine	Seed (cold stratification helps); division	Full sun; drought-tolerant; midsummer to fall bloom	Aster yellows (phytoplasma); Japanese beetles	Native prairie plant; spiny cone of disk florets; seeds feed goldfinches
Cork oak (Quercus suber)	Fagaceae	Evergreen tree; perennial	Bark (cork = phellem from the cork cambium)	Seed (acorns)	Mediterranean climate	Few major pests	Bark stripped about every 9 years without killing the tree; Portugal produces about half the world's cork
Corn (maize) (Zea mays)	Poaceae	Grass; warm-season annual	Grain (caryopsis); sweet corn = immature kernels; also silage, oil, starch, ethanol	Seed, after soil reaches about 50 °F	Frost-tender; heavy N feeder; plant in blocks, not one long row, for wind pollination; growing degree days use a 50 °F base	European corn borer; corn earworm; corn rootworm; common smut (Ustilago maydis)	C4; monoecious (tassel = male, ear = female; silks are styles); prop roots; domesticated from teosinte in southern Mexico about 9,000 years ago; sweet corn genes su, se, sh2; Bt corn; one of the Three Sisters
Cotton (Gossypium hirsutum, upland)	Malvaceae	Shrubby perennial grown as warm-season annual	Seed hairs (lint = epidermal trichomes) from the boll (capsule); cottonseed oil and meal	Seed	Long, hot, frost-free season; full sun	Boll weevil (now eradicated from most of the U.S.); bollworms; Verticillium and Fusarium wilts	Most-used plant textile fiber; Bt cotton widespread; seeds contain toxic gossypol; Pima (G. barbadense) is extra-long staple; U.S. paper currency is 75% cotton, 25% linen
Cowpea (black-eyed pea) (Vigna unguiculata)	Fabaceae	Herbaceous; warm-season annual	Seeds; immature pods; leaves	Seed	Heat- and drought-tolerant; grows on poor soils	Cowpea curculio; aphids; root-knot nematodes	Origin West Africa; Southern U.S. New Year's dish; N-fixing
Crabapple (Malus spp.)	Rosaceae	Deciduous small tree; perennial	Ornamental (flowers, fruit); pollinizer for apples	Budding, grafting	Full sun; hardy	Apple scab; fire blight; cedar-apple rust (choose resistant cultivars)	Fruit 2 in. or less across; widely planted in orchards as pollinizers
Cranberry (Vaccinium macrocarpon)	Ericaceae	Low evergreen woody trailing vine; perennial	Fruit (berry from an inferior ovary)	Stem cuttings (runners) pressed into bog sand	Acid, sandy bogs; flooded for wet harvest (fruits float on internal air pockets) and winter protection	Cranberry fruitworm; fruit rots	Native to North America; Wisconsin leads production; one of few native commercial fruits
Crape myrtle (Lagerstroemia indica)	Lythraceae	Deciduous shrub or small tree; perennial	Ornamental (summer flowers, peeling bark)	Cuttings	Heat-loving, full sun; about zones 7 to 9; blooms on new wood	Powdery mildew; crape myrtle bark scale; aphids (sooty mold)	Over-pruning to stubs is called "crape murder"; origin China and Korea
Crocus (Crocus vernus and others)	Iridaceae	Monocot corm; perennial	Ornamental (early spring flowers)	Cormels; seed	Plant corms in fall; needs winter chilling	Squirrels and voles eat corms	Among the first spring bulbs; saffron crocus is a different, fall-blooming species
Cucumber (Cucumis sativus)	Cucurbitaceae	Herbaceous vine with tendrils; warm-season annual	Fruit (immature pepo)	Seed or transplants, about 2 to 3 weeks after last frost	Frost-tender; trellis; monoecious (male flowers appear first), bees; gynoecious hybrids need a pollinizer; greenhouse ("English") types are parthenocarpic	Striped and spotted cucumber beetles (spread bacterial wilt, Erwinia tracheiphila); cucumber mosaic virus; powdery and downy mildew	Bitterness from cucurbitacins; DN; origin India
Currant and gooseberry (Ribes spp.)	Grossulariaceae	Deciduous shrub; perennial	Fruit (berry)	Hardwood cuttings; layering	Cool climates; tolerates part shade; self-fruitful	Imported currantworm; powdery mildew; currant aphid	Alternate host of white pine blister rust, so planting was banned federally (from about 1911 to 1966) and some states still restrict it; black currants high in vitamin C
Daffodil (Narcissus spp.)	Amaryllidaceae	Monocot bulb (tunicate); perennial	Ornamental (spring flowers)	Offset bulbs (division)	Plant in fall about 6 in. deep; needs chilling; let leaves die back naturally to refill the bulb	Narcissus bulb fly; basal rot (Fusarium)	All parts toxic (lycorine), so deer and rodents avoid them; trumpet is the corona
Dahlia (Dahlia hybrids)	Asteraceae	Herbaceous perennial from tuberous roots	Ornamental (flower heads, cut flower)	Division of tuberous roots (each needs a piece of crown with an eye); cuttings; seed	Warm-season, full sun; frost-tender, so dig after first frost and store cool and dry	Earwigs; slugs; powdery mildew; spider mites	National flower of Mexico; textbook example of a tuberous root
Date palm (Phoenix dactylifera)	Arecaceae	Palm (monocot tree); perennial	Fruit (berry)	Offshoots (suckers) to keep cultivars true; tissue culture	Hot, dry air with irrigation ("feet in water, head in the fire")	Bayoud disease (Fusarium); red palm weevil	Dioecious; hand pollination of female trees; origin Middle East and North Africa
Daylily (Hemerocallis spp.)	Asphodelaceae	Herbaceous monocot perennial with fleshy roots	Ornamental (flowers)	Division	Sun to part shade; very tough; each flower lasts one day	Daylily rust; aphids; thrips	Not a true lily; toxic to cats; diploid and tetraploid cultivars
Dieffenbachia (dumb cane) (Dieffenbachia spp.)	Araceae	Herbaceous tropical perennial; houseplant	Ornamental (foliage)	Cane (stem) cuttings; air layering	Low to medium light; warm	Mealybugs; spider mites; bacterial soft rot	Calcium oxalate raphides make the mouth and tongue swell ("dumb cane")
Dill (Anethum graveolens)	Apiaceae	Herbaceous annual	Leaves (dill weed); fruit, a schizocarp ("dill seed")	Seed, direct-sown (dislikes transplanting)	Cool to warm; full sun; self-sows	Aphids; caterpillars of black swallowtail (host plant)	Umbels attract beneficial insects
Dogwood, flowering (Cornus florida)	Cornaceae	Deciduous understory tree; perennial	Ornamental (spring bracts, red fruit, fall color)	Softwood cuttings; grafting; seed	Part shade; acidic, well-drained soil	Dogwood anthracnose (Discula destructiva); powdery mildew; borers	White "petals" are four bracts around a cluster of tiny flowers; fruit a drupe; Virginia state tree and flower
Eggplant (Solanum melongena)	Solanaceae	Herbaceous perennial grown as warm-season annual	Fruit (berry)	Seed, started indoors and transplanted	Needs the most heat of the common nightshade crops; frost-tender	Flea beetles; Colorado potato beetle; Verticillium wilt	Old World origin (India, Southeast Asia)
Elm, American (Ulmus americana)	Ulmaceae	Deciduous vase-shaped tree; perennial	Shade and street tree	Seed; cuttings or grafts of resistant cultivars ('Princeton', 'Valley Forge')	Tolerant of urban conditions	Dutch elm disease (Ophiostoma, spread by elm bark beetles, a vascular wilt); elm yellows (phytoplasma)	Dutch elm disease killed most U.S. street elms after about 1930; fruit a samara
English ivy (Hedera helix)	Araliaceae	Evergreen woody vine; perennial	Ornamental groundcover, houseplant	Stem cuttings	Shade-tolerant; climbs with aerial (adventitious) roots	Bacterial leaf spot; spider mites (indoors)	Juvenile lobed climbing shoots vs adult unlobed flowering shoots (phase change); invasive in many U.S. forests; berries toxic
Fennel (Foeniculum vulgare)	Apiaceae	Herbaceous perennial, often grown as annual	Swollen leaf bases ("bulb," Florence fennel); leaves; fruit, a schizocarp ("seed")	Seed	Cool to warm; full sun	Aphids; swallowtail caterpillars	Anise flavor (anethole); often said to inhibit nearby plants (allelopathy claims are weakly supported), so usually planted apart; invasive in California
Fig (Ficus carica)	Moraceae	Deciduous tree or large shrub; perennial	Syconium (multiple fruit: fleshy hollow receptacle lined with tiny flowers)	Hardwood cuttings; layering	About zones 7 to 10; full sun; common figs set fruit without pollination	Fig rust; root-knot nematodes; fig mosaic; birds	Smyrna types need caprification by the fig wasp (Blastophaga psenes); milky latex irritates skin; one of the earliest domesticated plants (Middle East)
Flax (Linum usitatissimum)	Linaceae	Herbaceous; cool-season annual	Stem bast (phloem) fibers, retted for linen; seeds (linseed oil, flaxseed)	Seed	Cool, moist; fiber flax pulled, not cut	Flax rust (Melampsora lini); flax wilt (Fusarium)	Flax rust is where H. H. Flor described gene-for-gene resistance; seeds rich in omega-3 (ALA); Fertile Crescent; fruit a capsule (boll)
Forsythia (Forsythia × intermedia)	Oleaceae	Deciduous shrub; perennial	Ornamental (yellow flowers before leaves in early spring)	Softwood cuttings; layering (branch tips root on contact)	Full sun; very hardy; prune right after flowering (blooms on old wood)	Few pests; gall	Easily forced indoors in late winter
Foxglove (Digitalis purpurea)	Plantaginaceae	Herbaceous biennial (leaf rosette year 1, flower spike year 2)	Ornamental; leaves, source of cardiac glycosides	Seed (self-sows)	Part shade; needs cold (vernalization) to flower	Powdery mildew; leaf spot	Digitalis glycosides (digitoxin; digoxin comes mainly from D. lanata) for heart failure (William Withering, 1785); all parts very toxic; bumblebee-pollinated
Gardenia (Gardenia jasminoides)	Rubiaceae	Evergreen shrub; perennial	Ornamental (fragrant white flowers)	Cuttings	Acid soil (pH about 5 to 6); humidity; steady temperatures (swings cause bud drop)	Whiteflies; mealybugs; sooty mold; iron chlorosis in alkaline soil	Coffee family; origin southern China and nearby East Asia
Garlic (Allium sativum)	Amaryllidaceae	Herbaceous monocot; perennial grown as annual	Compound bulb of cloves (each clove is an axillary bud with a thick storage leaf)	Individual cloves, planted in fall; true seed is rare	Needs cold to form bulbs; harvest early to midsummer when lower leaves brown; cure before storage	White rot (Sclerotium cepivorum); onion thrips; stem and bulb nematode	Allicin forms when crushing mixes alliin with the enzyme alliinase; hardneck types send up scapes with bulbils; origin Central Asia
Geranium (zonal) (Pelargonium × hortorum)	Geraniaceae	Herbaceous tender perennial grown as annual	Ornamental (flowers)	Stem cuttings; seed	Full sun; frost-tender	Bacterial blight (Xanthomonas); botrytis; geranium budworm	Hardy "true geraniums" (cranesbills) are genus Geranium; fruit a beaked schizocarp; South Africa
Ginger (Zingiber officinale)	Zingiberaceae	Herbaceous monocot; perennial	Rhizome	Rhizome pieces with buds	Tropical; part shade; rich, moist, well-drained soil	Bacterial wilt (Ralstonia); soft rot	Pungency from gingerol; origin South and Southeast Asia; India the top producer
Ginkgo (Ginkgo biloba)	Ginkgoaceae	Deciduous gymnosperm tree; perennial	Shade and street tree; seeds eaten in Asia; leaf extracts	Grafting or cuttings of male clones; seed	Very tolerant of pollution, salt and compaction; few pests	Almost none	Dioecious; plant males, since female seeds have a foul fleshy coat (butyric acid); fan leaves with forked (dichotomous) veins; only living species of its phylum ("living fossil")
Gladiolus (Gladiolus hybrids)	Iridaceae	Monocot corm; perennial	Ornamental (cut flower spikes)	Cormels	Plant in succession in spring; tender, dig in fall in the North	Gladiolus thrips; Fusarium corm rot	Flowers on a spike; origin South Africa
Grape (Vitis vinifera, European; V. labrusca, Concord; V. rotundifolia, muscadine)	Vitaceae	Deciduous woody vine climbing by tendrils; perennial	Fruit (berry), in clusters	Hardwood cuttings; vinifera grafted onto phylloxera-resistant American rootstocks	Full sun, well-drained; fruit on shoots from 1-year-old canes; heavy dormant pruning (cane or spur); most self-fruitful (some muscadines female, need pollinizer)	Phylloxera (root aphid); powdery mildew (Erysiphe necator); downy mildew (Plasmopara viticola); Pierce's disease (Xylella fastidiosa, xylem-clogging bacterium spread by sharpshooters)	Bordeaux mixture invented for downy mildew; seedless table grapes by stenospermocarpy, sized up with gibberellin sprays; non-climacteric; origin Caucasus and Near East
Grapefruit (Citrus × paradisi)	Rutaceae	Evergreen tree; perennial	Fruit (hesperidium)	Budded onto citrus rootstocks (sour orange, Swingle citrumelo and others)	Frost-tender, about zones 9 to 11; self-fruitful	Citrus greening (huanglongbing, spread by Asian citrus psyllid); citrus canker	Pomelo × sweet orange hybrid found in Barbados (1700s); furanocoumarins interfere with many drugs
Hazelnut (filbert) (Corylus avellana)	Betulaceae	Deciduous shrub or small tree; perennial	Nut (in a leafy husk)	Layering; suckers; grafting	Mild, wet winters; monoecious, wind-pollinated in midwinter; self-incompatible, needs pollinizers	Eastern filbert blight (Anisogramma anomala); filbertworm	Oregon's Willamette Valley grows nearly all U.S. hazelnuts; Turkey leads the world
Hemp (Cannabis sativa)	Cannabaceae	Herbaceous; warm-season annual	Stem bast fibers (retted); seeds (oil, food); flowers (CBD)	Seed	SD; full sun	Gray mold (Botrytis); hemp russet mite	Mostly dioecious (monoecious cultivars exist); U.S. industrial hemp must contain under 0.3% THC (2018 Farm Bill)
Holly (Ilex opaca, American; I. aquifolium, English)	Aquifoliaceae	Evergreen tree or shrub; perennial	Ornamental (spiny leaves, red drupes)	Cuttings; seed (slow)	Acid soil; sun to part shade	Holly leafminer; scale; leaf spot	Dioecious: females bear fruit only with a male nearby; berries toxic
Hops (Humulus lupulus)	Cannabaceae	Herbaceous perennial bine (twines, climbs with hooked hairs)	Female inflorescences ("cones," strobiles) with lupulin glands	Rhizome cuttings	Tall trellises (about 18 ft); flowers as days shorten; grown about 35 to 55° latitude	Downy mildew (Pseudoperonospora humuli); powdery mildew; spider mites; hop aphid	Dioecious; only unpollinated female plants grown; bitter acids flavor and preserve beer; Yakima Valley, Washington leads U.S.
Horseradish (Armoracia rusticana)	Brassicaceae	Herbaceous perennial	Taproot	Root cuttings ("sets"); rarely sets viable seed	Cool, hardy; spreads and can become weedy	Flea beetles; root rots	Heat from allyl isothiocyanate (from sinigrin); wasabi is a different plant
Hosta (Hosta spp.)	Asparagaceae	Herbaceous perennial	Ornamental (foliage)	Division	Shade-tolerant; moist soil	Slugs; deer; Hosta virus X	Origin Japan, China and Korea; top-selling shade perennial
Hyacinth (Hyacinthus orientalis)	Asparagaceae	Monocot bulb (tunicate); perennial	Ornamental (fragrant spring flowers)	Offsets; bulblets made by scooping or scoring the basal plate	Fall-planted; needs chilling; easily forced in water	Bulb rots; bulb mites	Bulbs irritate skin (calcium oxalate)
Hydrangea, bigleaf (Hydrangea macrophylla)	Hydrangeaceae	Deciduous shrub; perennial	Ornamental (flower heads)	Softwood cuttings	Part shade, moist soil; most bloom on old wood (rebloomers also on new)	Powdery mildew; leaf spots	Color depends on soil pH through aluminum uptake: acid soil = blue, alkaline = pink (white types do not change); showy parts are sepals of sterile flowers; mophead and lacecap types
Impatiens (Impatiens walleriana)	Balsaminaceae	Herbaceous tender perennial grown as annual	Ornamental (bedding flowers)	Seed; cuttings	Shade; frost-tender; moist soil	Impatiens downy mildew (Plasmopara obducens, epidemic from about 2011)	Explosive capsules ("touch-me-not"); New Guinea impatiens are resistant to the downy mildew
Iris, bearded (Iris × germanica)	Iridaceae	Herbaceous monocot perennial from a rhizome	Ornamental (flowers)	Division of rhizomes after bloom (mid to late summer)	Full sun; plant rhizome at the soil surface	Iris borer; bacterial soft rot	Falls are sepals, standards are petals, the "beard" is on the falls; Siberian iris has fibrous roots; fleur-de-lis
Jade plant (Crassula ovata)	Crassulaceae	Succulent shrub; perennial houseplant	Ornamental	Leaf or stem cuttings	Bright light; let soil dry between waterings	Mealybugs; root rot	CAM; South Africa
Jatropha (Jatropha curcas)	Euphorbiaceae	Shrub or small tree; perennial	Seeds (oil for biodiesel)	Cuttings; seed	Drought-tolerant; grows on marginal land; tropical	Few serious pests	Seeds toxic (curcin, phorbol esters), so oil is not edible; used as living fences; origin Central America
Jerusalem artichoke (sunchoke) (Helianthus tuberosus)	Asteraceae	Herbaceous perennial	Stem tubers (store inulin, not starch)	Tubers	Hardy; full sun; spreads aggressively	Few pests	Native to North America; a sunflower, neither an artichoke nor from Jerusalem
Juniper, eastern redcedar (Juniperus virginiana)	Cupressaceae	Evergreen conifer tree; perennial	Aromatic wood (chests, pencils); fleshy seed cones ("berries") eaten by birds	Seed; cuttings	Very drought-tolerant; invades prairies when fire is suppressed	Bagworms	Alternate host of cedar-apple rust (Gymnosporangium juniperi-virginianae: galls with orange jelly horns in spring); dioecious; gin is flavored with common juniper (J. communis)
Jute (Corchorus capsularis, C. olitorius)	Malvaceae	Herbaceous; annual	Stem bast fibers, retted	Seed	Warm, humid monsoon climate; flooded lowlands	Stem rot; jute hairy caterpillar	"Golden fiber"; burlap and gunny sacks; India and Bangladesh grow most of it
Kalanchoe (Kalanchoe blossfeldiana)	Crassulaceae	Succulent; perennial potted plant	Ornamental (flowers)	Stem cuttings	SD (classic greenhouse short-day crop); bright light	Mealybugs; powdery mildew	CAM; related K. daigremontiana forms plantlets on leaf margins (vegetative reproduction)
Kale and collards (Brassica oleracea, Acephala and Viridis groups)	Brassicaceae	Herbaceous; biennial grown as annual	Leaves	Seed; transplants	Very cold-hardy; sweeter after frost (starch converts to sugar)	Cabbageworms; aphids; flea beetles	Close to wild cabbage, with no head; collards are a heat-tolerant Southern staple
Kentucky bluegrass (Poa pratensis)	Poaceae	Turf grass; cool-season perennial	Leaves (lawns, pastures)	Seed; sod	Full sun; goes dormant in summer heat and drought; self-repairs by rhizomes	Leaf spot and melting-out; dollar spot; white grubs	C3; seed often forms by apomixis; native to Europe and northern Asia despite the name
Kiwifruit (Actinidia deliciosa)	Actinidiaceae	Deciduous woody twining vine; perennial	Fruit (berry)	Grafting; cuttings	Needs chilling; sturdy trellis; frost-sensitive in spring	Bacterial canker (Psa, Pseudomonas syringae pv. actinidiae)	Dioecious: about one male vine per 6 to 8 females; origin China ("Chinese gooseberry"); commercialized in New Zealand
Kohlrabi (Brassica oleracea, Gongylodes group)	Brassicaceae	Herbaceous; biennial grown as annual	Swollen stem above ground	Seed; transplants	Cool-season; fast; harvest at 2 to 3 in.	Cabbageworms; flea beetles; clubroot	A stem, not a root
Kudzu (Pueraria montana var. lobata)	Fabaceae	Semi-woody perennial vine	Once planted for erosion control and forage; starchy roots	Rooting runners; crowns	Warm, humid Southeast U.S.; grows up to about a foot a day in summer	Kudzu bug	Promoted by the Soil Conservation Service in the 1930s; once on the federal noxious weed list (late 1990s) and still a state-listed noxious weed in many states; N-fixing
Lavender, English (Lavandula angustifolia)	Lamiaceae	Evergreen woody subshrub; perennial	Flower spikes (essential oil: linalool, linalyl acetate)	Softwood and semi-hardwood cuttings	Full sun; lean, well-drained, neutral to alkaline soil; drought-tolerant xeriscape plant	Root rot in wet soil	Mediterranean origin; Provence, France
Leek (Allium ampeloprasum, Porrum group)	Amaryllidaceae	Herbaceous monocot; biennial grown as annual	Pseudostem (rolled leaf sheaths), blanched by hilling or trenching	Seed, transplanted	Long, cool season; cold-hardy	Onion thrips; leek moth	National emblem of Wales
Lemon (Citrus × limon)	Rutaceae	Evergreen tree; perennial	Fruit (hesperidium)	Budding onto citrus rootstocks; cuttings	Very frost-tender; flowers and fruits much of the year	Citrus greening; scale; citrus canker	'Eureka', 'Lisbon'; 'Meyer' is a hybrid of citron with mandarin-type citrus, not a true lemon; lemon juice prevented scurvy (James Lind, 1747)
Lentil (Lens culinaris)	Fabaceae	Herbaceous; cool-season annual	Seeds (pulse)	Seed	Semi-arid, cool; drought-tolerant	Ascochyta blight; aphids	The lens-shaped seed named the optical lens; Fertile Crescent founder crop; Canada leads exports
Lettuce (Lactuca sativa)	Asteraceae	Herbaceous; cool-season annual	Leaves (crisphead/iceberg, butterhead, romaine, loose-leaf)	Seed (many cultivars need light to germinate; dormant above about 80 °F)	Cool; bolts and turns bitter in heat and long days (LD); common hydroponic crop	Aphids; downy mildew (Bremia lactucae); lettuce mosaic virus; slugs	Tipburn is calcium deficiency; milky latex; 'Grand Rapids' seed used in the red/far-red phytochrome experiments; origin Mediterranean and Egypt
Lilac (Syringa vulgaris)	Oleaceae	Deciduous shrub; perennial	Ornamental (fragrant spring flowers)	Suckers; softwood cuttings; grafting	Needs winter chilling; full sun; neutral to alkaline soil; prune right after flowering	Powdery mildew; lilac borer; bacterial blight	New Hampshire state flower
Lily (Lilium spp.; Easter lily L. longiflorum)	Liliaceae	Monocot scaly bulb (non-tunicate); perennial	Ornamental (flowers)	Bulb scales (scaling); bulbils (tiger lily); bulblets	Sun on top, cool roots; Easter lilies forced for spring	Lily leaf beetle; botrytis; viruses (aphids)	Extremely toxic to cats (kidney failure); most U.S. Easter lily bulbs come from the California-Oregon border
Lily of the valley (Convallaria majalis)	Asparagaceae	Herbaceous monocot perennial from a rhizome	Ornamental (fragrant flowers); groundcover	Division of rhizomes ("pips")	Shade; spreads aggressively	Few pests	All parts toxic (cardiac glycosides such as convallatoxin)
Lime (Citrus × aurantiifolia, Key lime; C. × latifolia, Persian)	Rutaceae	Evergreen tree; perennial	Fruit (hesperidium)	Budding; cuttings; air layering	Key lime is among the most cold-sensitive citrus	Citrus greening; citrus canker	Persian (Tahiti) lime is a seedless triploid
Lotus, sacred (Nelumbo nucifera)	Nelumbonaceae	Aquatic herbaceous perennial	Rhizome; seeds; ornamental flowers	Rhizome division; seed (scarify)	Shallow warm ponds; full sun	Aphids	Seeds stayed viable about 1,300 years; leaves shed water (lotus effect); flowers make heat (thermogenic); not a water lily
Luffa (loofah) (Luffa aegyptiaca)	Cucurbitaceae	Herbaceous vine; warm-season annual	Mature fruit (pepo) retted to its fibrous vascular network (sponge); young fruit eaten	Seed	Long, hot season; trellis	Cucumber beetles; powdery mildew	The "sponge" is the fruit's fibrous vascular skeleton
Lychee (Litchi chinensis)	Sapindaceae	Evergreen tree; perennial	Aril (white flesh around the seed)	Air layering (marcotting); grafting	Subtropical; needs a cool, dry winter to flower	Lychee erinose mite; fruit borers	Related longan and rambutan also have arils; origin southern China
Macadamia (Macadamia integrifolia, M. tetraphylla)	Proteaceae	Evergreen tree; perennial	Seed (kernel) in a very hard shell, from a follicle	Grafting	Subtropical, frost-sensitive	Macadamia felted coccid; nut borers	Origin eastern Australia (Queensland and northern New South Wales); commercialized in Hawaii; toxic to dogs
Madagascar periwinkle (Catharanthus roseus)	Apocynaceae	Herbaceous tender perennial grown as annual ("annual vinca")	Ornamental; leaves yield vinblastine and vincristine	Seed; cuttings	Heat- and drought-tolerant; full sun	Phytophthora aerial blight; root rot in wet soil	Vincristine treats childhood leukemia; vinblastine Hodgkin lymphoma; endemic to Madagascar; toxic; not the groundcover Vinca minor
Magnolia, southern (Magnolia grandiflora)	Magnoliaceae	Evergreen tree; perennial	Ornamental (large white flowers)	Seed; cuttings; grafting	Warm, humid Southeast; acid soil	Magnolia scale; leaf spots	Beetle-pollinated; tepals (sepals and petals alike); aggregate of follicles with red seeds; Mississippi state tree and flower
Mandarin and tangerine (Citrus reticulata)	Rutaceae	Evergreen tree; perennial	Fruit (hesperidium, loose peel)	Budding onto citrus rootstocks	Satsuma mandarins are among the most cold-hardy edible citrus	Citrus greening; scale; mites	One of the ancestral citrus species (with pomelo and citron); 'Clementine' is seedless when isolated from pollinizers
Mango (Mangifera indica)	Anacardiaceae	Evergreen tree; perennial	Fruit (drupe)	Veneer or cleft grafting onto seedling rootstock; polyembryonic types come true from seed (nucellar embryos)	Tropical or subtropical; a dry season triggers flowering; frost-tender	Anthracnose (Colletotrichum); powdery mildew; mango malformation	Sap and peel contain urushiol-like compounds (rash); origin India, which is the top producer
Maple, sugar (Acer saccharum)	Sapindaceae	Deciduous tree; perennial	Xylem sap (maple syrup); timber	Seed	Tap in late winter when freezing nights alternate with thawing days; about 40 gal sap per 1 gal syrup	Tar spot; Verticillium wilt; Asian longhorned beetle	Fruit a double samara (schizocarp); state tree of New York, Vermont, West Virginia and Wisconsin; Quebec makes most of the world's syrup
Marigold (Tagetes erecta, African; T. patula, French)	Asteraceae	Herbaceous; warm-season annual	Ornamental (flower heads); petals for dyes and poultry feed pigment	Seed (easy)	Full sun; heat-tolerant; frost-tender	Spider mites; botrytis; slugs	Roots of French marigold suppress root-knot nematodes (alpha-terthienyl); native to Mexico and Central America despite the names; Day of the Dead flower; pot marigold (Calendula) is a different genus (same family, Asteraceae)
Millet, pearl (Cenchrus americanus, formerly Pennisetum glaucum)	Poaceae	Grass; warm-season annual	Grain (caryopsis)	Seed	The most heat- and drought-tolerant cereal; sandy, poor soils (Sahel, India)	Downy mildew (Sclerospora graminicola); ergot	C4; origin West Africa
Mint (Mentha × piperita, peppermint; M. spicata, spearmint)	Lamiaceae	Herbaceous perennial	Leaves (menthol in peppermint, carvone in spearmint)	Rhizome and stolon division; cuttings (peppermint is a sterile hybrid)	Moist soil, sun to part shade; very invasive, so grow in containers	Mint rust (Puccinia menthae); Verticillium wilt	Square stems, opposite leaves; said to repel ants; Idaho, Oregon and Washington lead U.S. mint oil production
Morning glory (Ipomoea purpurea, I. tricolor)	Convolvulaceae	Herbaceous twining vine; warm-season annual	Ornamental (flowers)	Seed (hard coat: nick or soak to scarify)	Full sun; frost-tender; flowers open in the morning and fade by afternoon	Aphids; leaf miners	Seeds toxic (ergoline alkaloids); sweet potato relative; field bindweed is a related weed
Mustard (Brassica juncea, brown; Sinapis alba, white; B. nigra, black)	Brassicaceae	Herbaceous; cool-season annual	Seeds (from siliques, the condiment); leaves (greens)	Seed	Cool; bolts in heat	Flea beetles; aphids	Pungency from glucosinolates (in brown and black mustard, sinigrin to allyl isothiocyanate; white mustard uses sinalbin); used as a biofumigant cover crop
Nasturtium (Tropaeolum majus)	Tropaeolaceae	Herbaceous annual (trailing or bushy)	Edible flowers and peppery leaves; ornamental	Seed (large; soak)	Full sun; poor soil gives more flowers (excess N gives leaves)	Aphids (used as a trap crop)	Round peltate leaves; spurred flowers; origin Andes; genus Nasturtium is watercress
Nutmeg and mace (Myristica fragrans)	Myristicaceae	Evergreen tropical tree; perennial	Seed (nutmeg) and its red aril (mace)	Seed; grafting to get known females	Humid tropics	Few serious pests	Dioecious (sex unknown until flowering); myristicin toxic in large doses; native to Indonesia's Banda Islands
Oak (Quercus alba, white; Q. rubra, red; others)	Fagaceae	Deciduous (live oaks evergreen) tree; perennial	Timber; acorns (nut in a cupule); shade tree	Seed (acorns cannot be dried)	Mostly full sun; long-lived	Oak wilt (Bretziella fagacearum); sudden oak death (Phytophthora ramorum); spongy (gypsy) moth; galls	Monoecious, wind-pollinated catkins; white oak acorns mature in one season, red oak in two; tannins; U.S. national tree (2004)
Oats (Avena sativa)	Poaceae	Grass; cool-season annual	Grain (caryopsis, a hulled "groat") in a panicle	Seed	Cool, moist; tolerates acid soil; a common nurse crop	Crown rust (Puccinia coronata; alternate host buckthorn); barley yellow dwarf	C3; LD; beta-glucan fiber
Oil palm (Elaeis guineensis)	Arecaceae	Palm (monocot tree); perennial	Fruit (drupe): palm oil from the mesocarp, palm kernel oil from the seed	Seed; tissue culture	Humid tropics	Basal stem rot (Ganoderma); rhinoceros beetles	World's most-produced vegetable oil; Indonesia and Malaysia grow most; plantations drive rainforest loss; weevil-pollinated; origin West Africa
Okra (Abelmoschus esculentus)	Malvaceae	Herbaceous; warm-season annual	Immature fruit (capsule, "pod"), picked 2 to 4 in. long	Seed (hard coat; soak), direct-sown in warm soil	Heat-loving; frost-tender	Root-knot nematodes; stink bugs; corn earworm	Mucilage thickens gumbo; hibiscus-like flowers; origin Africa
Olive (Olea europaea)	Oleaceae	Evergreen tree; perennial, can live over 1,000 years	Fruit (drupe; oil from the mesocarp)	Cuttings; grafting	Mediterranean climate: mild winter chill for flowering, hot dry summer; wind-pollinated; alternate bearing	Olive fruit fly; olive knot (Pseudomonas savastanoi); Xylella fastidiosa (Italy); Verticillium wilt	Bitter oleuropein removed by curing (lye or brine); Spain the top producer
Onion (Allium cepa)	Amaryllidaceae	Herbaceous monocot; biennial grown as annual	Bulb (tunicate: fleshy leaf bases on a short stem, the basal plate)	Seed; sets (small bulbs); transplants	Cool-season, frost-hardy; bulbing is triggered by day length: short-day cultivars (South), intermediate, long-day (North); cure tops dry before storage	Onion thrips; onion maggot; pink root; neck rot (Botrytis)	Tearing from syn-propanethial-S-oxide; low-sulfur soils make sweet onions (Vidalia); epidermis is a standard microscope lab
Opium poppy (Papaver somniferum)	Papaveraceae	Herbaceous; annual	Latex from the unripe capsule (morphine, codeine, thebaine); seeds (culinary)	Seed	Cool-season; full sun	Downy mildew	Latex in laticifers; capsule opens by pores; source of all natural opiates
Orange, sweet (Citrus × sinensis)	Rutaceae	Evergreen tree; perennial	Fruit (hesperidium; juice sacs grow from the endocarp)	Budding onto rootstocks (sour orange, trifoliate orange hybrids); nucellar seedlings	Subtropical, frost-tender (about zones 9 to 11); self-fruitful; 7 to 12 months from bloom to harvest; fruit stores on the tree	Citrus greening (HLB; Asian citrus psyllid); citrus canker; tristeza virus; Phytophthora	Non-climacteric; navel oranges are seedless (parthenocarpic) clones of one Brazilian mutation; Brazil the top producer; ancestry a mandarin × pomelo hybrid, mostly mandarin
Orchid, moth (Phalaenopsis hybrids)	Orchidaceae	Epiphytic monocot; perennial	Ornamental (flowers); top U.S. potted flowering plant by wholesale value	Tissue culture (mericloning); keikis (plantlets on the flower stalk)	Bright indirect light; bark media; cool nights trigger flower spikes	Mealybugs; scale; crown rot	Dust-like seeds lack endosperm and need mycorrhizal fungi (or sterile agar) to germinate; aerial roots with velamen; CAM; pollinia; lip (labellum) and column
Oregano (Origanum vulgare)	Lamiaceae	Herbaceous perennial	Leaves	Cuttings; division; seed	Full sun; lean, dry soil	Root rot in wet soil; aphids	Carvacrol and thymol; Mediterranean
Pansy (Viola × wittrockiana)	Violaceae	Herbaceous; short-lived perennial grown as cool-season annual	Ornamental (flowers; edible)	Seed	Frost-tolerant; fall and winter bedding plant in the South	Downy mildew; anthracnose; slugs	Nectar guides on the petals
Papaya (Carica papaya)	Caricaceae	Large, fast, short-lived tree-like herb; perennial	Fruit (berry)	Seed	Tropical, frost-free	Papaya ringspot virus (aphids); fruit flies	Plants are female, male or hermaphrodite; transgenic virus-resistant 'Rainbow' and 'SunUp' (1998) saved Hawaii's papaya industry; papain (latex enzyme) tenderizes meat
Parsley (Petroselinum crispum)	Apiaceae	Herbaceous; biennial grown as annual	Leaves (curly or flat Italian); root in root parsley	Seed (slow, 3 to 4 weeks; soak)	Cool-season; sun to part shade	Black swallowtail caterpillars; carrot rust fly	Umbel flowers in the second year
Parsnip (Pastinaca sativa)	Apiaceae	Herbaceous; biennial grown as annual	Taproot	Seed (must be fresh; short-lived)	Long, cool season; frost turns starch to sugar, so harvest after frost or in spring	Carrot rust fly; canker	Wild parsnip sap causes phytophotodermatitis (furanocoumarins)
Passion flower (Passiflora incarnata; P. edulis passion fruit)	Passifloraceae	Herbaceous or woody tendril vine; perennial	Ornamental; fruit (berry, juicy arils around seeds)	Seed; cuttings	Full sun; P. incarnata hardy, passion fruit frost-tender	Nematodes; viruses; fungal leaf spots	Corona of filaments; host plant of gulf fritillary butterflies
Pawpaw (Asimina triloba)	Annonaceae	Deciduous understory tree; perennial	Fruit (berry)	Seed (cold stratification); grafting	Part shade when young; needs 2 cultivars for cross-pollination	Few pests	Largest edible fruit native to North America; maroon flowers pollinated by flies and beetles; host of zebra swallowtail
Pea, garden (Pisum sativum)	Fabaceae	Herbaceous vine climbing by tendrils (modified leaflets); cool-season annual	Seeds (shelling peas); edible immature pods (snow, snap)	Seed, sown as soon as the soil can be worked in early spring	Cool, frost-tolerant; stops producing in heat; self-pollinating	Powdery mildew; aphids; Fusarium wilt; pea enation mosaic	Mendel's genetics organism; hypogeal germination; N-fixing; Fertile Crescent
Peach and nectarine (Prunus persica)	Rosaceae	Deciduous tree; perennial, short-lived (about 15 to 20 years)	Fruit (drupe; clingstone or freestone)	Budding onto seedling peach rootstocks ('Lovell', nematode-resistant 'Nemaguard')	Needs chilling (low-chill cultivars for the South); most self-fruitful; fruits on 1-year-old wood; open-center (vase) pruning	Peach leaf curl (Taphrina deformans); brown rot (Monilinia fructicola); plum curculio; peach tree borer	Nectarine = a recessive fuzzless mutation; climacteric; origin China; California leads U.S. production
Peanut (Arachis hypogaea)	Fabaceae	Herbaceous; warm-season annual	Seeds from a pod (legume) that matures underground	Seed	Long warm season; sandy, well-drained soil; calcium (gypsum) for pod fill; self-pollinating	Leaf spots (Cercospora); white mold (Sclerotium rolfsii); aflatoxin (Aspergillus flavus)	After pollination the peg (gynophore) pushes the ovary into the soil (geocarpy); C3; N-fixing; George Washington Carver; origin South America; Georgia leads U.S.
Pear (Pyrus communis, European; P. pyrifolia, Asian)	Rosaceae	Deciduous tree; perennial	Fruit (pome) with grit (stone cells = sclereids)	Grafted onto pear seedlings, 'OH×F' clones or quince (dwarfing)	Needs chilling; most need a pollinizer; European pears are picked mature but hard and ripened off the tree; Asian pears ripen on the tree	Fire blight (very susceptible); pear psylla; codling moth	Pacific Northwest leads U.S.; 'Bartlett'
Pear, Callery ('Bradford') (Pyrus calleryana)	Rosaceae	Deciduous ornamental tree; perennial	Ornamental (white spring flowers)	Grafted cultivars	Tolerant of urban sites; weak, narrow crotches split in storms	Fairly fire-blight-resistant	Flowers smell foul; different cultivars cross-pollinate, so seedlings form invasive thorny thickets; banned from sale in Ohio and some other states
Pecan (Carya illinoinensis)	Juglandaceae	Deciduous tree; perennial	Seed of a drupe-like nut (hard shell inside a splitting husk)	Budding or grafting onto seedling pecan rootstock	Long, hot season; monoecious, wind-pollinated, with protandrous and protogynous cultivars (plant both types); alternate bearing	Pecan scab; pecan weevil; hickory shuckworm; zinc deficiency (rosette)	Native to the Mississippi valley and Texas; Texas state tree; Georgia and New Mexico lead U.S.
Peony (Paeonia lactiflora; tree peonies)	Paeoniaceae	Herbaceous perennial with tuberous roots (tree peony is woody)	Ornamental (flowers; cut flower)	Division in fall, buds ("eyes") no more than about 2 in. deep (deeper = no flowers)	Needs winter chilling; full sun	Botrytis blight; ants on buds (harmless, attracted to nectar)	Very long-lived; Indiana state flower; fruit an aggregate of follicles
Pepper (bell and chili) (Capsicum annuum; C. chinense, habanero)	Solanaceae	Herbaceous perennial grown as warm-season annual	Fruit (berry); bell peppers eaten green (unripe) or ripe	Seed, started indoors and transplanted	Warmer soil than tomato; flowers drop in extreme heat or cold	Blossom-end rot (calcium); bacterial leaf spot; Phytophthora blight; aphids	Capsaicin is concentrated in the placenta ("ribs"), measured in Scoville units; origin Mexico and South America
Persimmon (Diospyros kaki, Asian; D. virginiana, American)	Ebenaceae	Deciduous tree; perennial	Fruit (berry with persistent calyx)	Grafted onto seedling rootstocks	Asian about zones 7 to 10; many cultivars set fruit without pollination	Few serious pests	Astringent types ('Hachiya') must be soft-ripe (tannins); non-astringent ('Fuyu') eaten firm; American persimmon is native
Petunia (Petunia × atkinsiana)	Solanaceae	Herbaceous tender perennial grown as annual	Ornamental (bedding, baskets)	Seed (tiny, needs light); cuttings	Full sun; frost-tender	Botrytis; tobacco budworm; aphids	RNA silencing (co-suppression) was discovered in petunia flower color (1990); among the first transgenic plants (1983); origin South America
Pine (Pinus strobus, eastern white; P. taeda, loblolly; others)	Pinaceae	Evergreen conifer tree; perennial	Timber and pulp; resin (turpentine, rosin); seeds (pine nuts from pinyon and stone pines); Christmas trees	Seed	Full sun; acid soils	White pine blister rust (Cronartium ribicola, alternate host Ribes); pine bark beetles	Needles in bundles (fascicles): white pine 5, loblolly 3, red pine 2; seed cones take about 2 years to mature; gymnosperm
Pineapple (Ananas comosus)	Bromeliaceae	Herbaceous monocot rosette; perennial	Multiple fruit (berries of many flowers fused with bracts and the axis)	Crowns, slips and suckers	Tropical; well-drained, acid soil; flowering forced with ethylene (ethephon) or calcium carbide	Mealybug wilt; Phytophthora heart rot	CAM; self-incompatible, so commercial fruit is seedless; bromelain enzyme; non-climacteric; origin South America (Paraguay, Brazil)
Pistachio (Pistacia vera)	Anacardiaceae	Deciduous tree; perennial	Seed of a semi-dry drupe; shell (endocarp) splits when ripe	Budded onto P. atlantica, P. integerrima or hybrid ('UCB-1') rootstocks	Hot, dry summers and cold winters (chilling); dioecious, wind-pollinated, about one male per 8 to 24 females; alternate bearing	Verticillium wilt; navel orangeworm; aflatoxin	Female 'Kerman', male 'Peters'; origin Iran and Central Asia; California leads U.S.
Plum (Prunus domestica, European; P. salicina, Japanese)	Rosaceae	Deciduous tree; perennial	Fruit (drupe); dried as prunes	Budding onto plum or peach rootstocks	European types often self-fruitful; Japanese types need a pollinizer; fruit on spurs of older wood, so prune lightly	Black knot (Apiosporina morbosa); brown rot; plum curculio; plum pox virus	European plum is hexaploid; prunes are dried European plums
Poinsettia (Euphorbia pulcherrima)	Euphorbiaceae	Woody shrub; perennial, grown as potted plant	Ornamental (red bracts around tiny cyathia)	Vegetative (stem) cuttings	SD: needs about 14 hr of uninterrupted darkness nightly for 8 to 10 weeks from about October 1; warm	Silverleaf whitefly; Pythium root rot; botrytis	Best-selling U.S. holiday potted plant by number (orchids now lead in wholesale value); milky latex irritates, but toxicity is overstated; origin Mexico; free-branching cultivars carry a phytoplasma
Pomegranate (Punica granatum)	Lythraceae	Deciduous shrub or small tree; perennial	Fleshy seed coats (sarcotesta) of the many seeds	Hardwood cuttings	Hot, dry summers; self-fruitful	Heart rot; leaf-footed bugs	Leathery fruit called a balausta; origin Iran
Potato (Solanum tuberosum)	Solanaceae	Herbaceous perennial grown as cool-season annual	Stem tuber (eyes are axillary buds in the axils of scale-leaf scars)	Certified "seed potatoes": tuber pieces about 1.5 to 2 oz, each with 1 to 2 eyes, cut and cured; true seed rarely	Cool-season; short days and cool nights favor tuber formation; hill soil over tubers; pH about 5.0 to 5.5 limits scab	Late blight (Phytophthora infestans, Irish famine 1845 to 1849); Colorado potato beetle; early blight; common scab (Streptomyces scabies); potato virus Y	Light makes tubers green (chlorophyll) and raises toxic glycoalkaloids (solanine); C3; berries toxic; origin Andes (Peru, Bolivia)
Pothos (Epipremnum aureum)	Araceae	Evergreen climbing vine; perennial houseplant	Ornamental (foliage)	Stem cuttings (root in water)	Low light tolerant; let soil dry	Root rot; mealybugs	Calcium oxalate, toxic to pets; potted plants usually stay in the small juvenile leaf form
Pumpkin (Cucurbita pepo, C. maxima, C. moschata)	Cucurbitaceae	Herbaceous vine; warm-season annual	Fruit (pepo); seeds (pepitas)	Seed after frost	Long, warm season; monoecious, bees (squash bees); cure before storage	Squash bug; squash vine borer; cucumber beetles; powdery mildew	Squash was among the first domesticated plants in the Americas (Mexico, about 10,000 years ago); giant pumpkins are C. maxima; one of the Three Sisters; Illinois leads U.S.
Quinoa (Chenopodium quinoa)	Amaranthaceae	Herbaceous; cool-season annual	Small dry fruit (achene), used as a pseudocereal	Seed	Tolerates cold, salt, drought and high altitude	Downy mildew (Peronospora variabilis)	Bitter saponins in the outer layers (pericarp and seed coat) are washed off; complete protein (all essential amino acids); origin Andes (Bolivia, Peru)
Radish (Raphanus sativus)	Brassicaceae	Herbaceous; cool-season annual (daikon types biennial)	Storage organ = swollen hypocotyl plus upper taproot	Seed, direct-sown	Fastest common crop (about 3 to 4 weeks); LD, bolts in summer; gets pithy if left too long	Flea beetles; cabbage root maggot	Often sown with slow carrots to mark rows; daikon used as "tillage radish" cover crop
Raspberry (Rubus idaeus, red; R. occidentalis, black)	Rosaceae	Perennial crown with biennial canes	Aggregate fruit of drupelets; pulls off the receptacle (hollow)	Suckers (red); tip layering (black and purple)	Summer-bearing types fruit on floricanes (2nd-year canes); fall-bearing (primocane) types fruit on 1st-year canes; trellis; self-fruitful	Phytophthora root rot; cane blights; anthracnose; spotted wing drosophila; viruses	Remove canes after they fruit
Redbud, eastern (Cercis canadensis)	Fabaceae	Deciduous understory tree; perennial	Ornamental (pink-purple flowers before leaves)	Seed (scarify and cold-stratify); grafting	Sun to part shade	Verticillium wilt; Botryosphaeria canker	Flowers on old wood and trunk (cauliflory); heart-shaped leaves; a legume that does not form root nodules; Oklahoma state tree
Rhubarb (Rheum × hybridum)	Polygonaceae	Herbaceous perennial	Petioles (leaf stalks); leaf blades are toxic (oxalic acid)	Division of crowns (each piece with a bud)	Needs winter cold (dormancy below about 40 °F); harvest in spring from the 2nd or 3rd year; remove flower stalks	Crown rot; rhubarb curculio	Botanically a vegetable, but a 1947 U.S. customs ruling classed it as a fruit
Rice (Oryza sativa, Asian; O. glaberrima, African)	Poaceae	Semi-aquatic grass; annual	Grain (caryopsis); brown rice keeps the bran, white rice is milled endosperm	Seed: direct-seeded or transplanted into flooded paddies	Warm, wet; flooding controls weeds; most cultivars SD	Rice blast (Magnaporthe oryzae); bacterial blight; sheath blight; brown planthopper	C3; aerenchyma carries O2 to roots; bakanae ("foolish seedling") disease led to discovery of gibberellin; IR8 semi-dwarf of the Green Revolution; Golden Rice (beta-carotene in the endosperm); first crop genome sequenced; feeds over half the world
Rose (Rosa spp. and hybrids)	Rosaceae	Woody shrub or climber; perennial	Ornamental (flowers; top U.S. cut flower); rose hips (accessory fruit, vitamin C)	T-budding onto rootstocks ('Dr. Huey', R. multiflora); own-root cuttings	Full sun (6+ hr); good air circulation; DN	Black spot (Diplocarpon rosae); powdery mildew; rose rosette virus (eriophyid mites); Japanese beetles	"Thorns" are prickles (epidermal outgrowths); Colombia and Ecuador supply most U.S. cut roses; U.S. national flower
Rosemary (Salvia rosmarinus)	Lamiaceae	Evergreen woody shrub; perennial	Leaves (needle-like)	Cuttings	Full sun; well-drained; drought-tolerant; hardy only to about zone 7 or 8	Root rot; powdery mildew; spittlebugs	Moved from Rosmarinus to Salvia in 2017; Mediterranean
Rubber tree, Pará (Hevea brasiliensis)	Euphorbiaceae	Tropical tree; perennial	Latex from laticifers in the bark (tapped)	Budding onto seedling rootstocks	Humid tropics	South American leaf blight (Pseudocercospora ulei) prevents Amazon plantations	Seeds taken from Brazil (Wickham, 1876) via Kew founded Southeast Asian plantations; Thailand and Indonesia lead; latex is cis-polyisoprene; houseplant "rubber plant" is Ficus elastica
Rutabaga (Brassica napus, Napobrassica group)	Brassicaceae	Herbaceous; biennial grown as annual	Storage root plus hypocotyl ("neck")	Seed	Long, cool season; stores well	Cabbage root maggot; clubroot	A turnip × cabbage cross (same species as canola); yellow flesh
Rye (Secale cereale)	Poaceae	Grass; cool-season annual (winter rye)	Grain (caryopsis); cover crop	Seed	The most winter-hardy cereal; poor, acid, sandy soils	Ergot (Claviceps purpurea)	Cross-pollinated (self-incompatible), so ergot is common; ergotism ("St. Anthony's fire"); allelopathic cover crop; triticale = wheat × rye
Saffron (Crocus sativus)	Iridaceae	Monocot corm; perennial	Dried stigmas (3 per flower)	Cormels only (sterile triploid)	Plant corms in late summer; blooms in fall; hot dry summers	Corm rots; rodents	Most expensive spice; about 150 flowers per gram; crocin color, safranal aroma; Iran grows about 90%
Sage (Salvia officinalis)	Lamiaceae	Woody subshrub; perennial	Leaves	Cuttings; layering; seed	Full sun; well-drained	Root rot; powdery mildew	Square stems; Mediterranean
Sesame (Sesamum indicum)	Pedaliaceae	Herbaceous; warm-season annual	Seeds (oil, food)	Seed	Hot; drought-tolerant	Phyllody (phytoplasma); leaf spots	Capsules shatter open when ripe (often linked to "open sesame"), so non-shattering cultivars help machine harvest; one of the oldest oilseeds; allergen
Sisal (Agave sisalana)	Asparagaceae	Succulent monocot rosette; perennial	Leaf fibers (hard fiber for twine, rope)	Bulbils; suckers	Arid tropics	Agave weevil	CAM; Brazil and Tanzania lead; henequen (A. fourcroydes) is a related fiber
Snake plant (Dracaena trifasciata, formerly Sansevieria)	Asparagaceae	Succulent rhizomatous monocot; perennial houseplant	Ornamental (foliage)	Division; leaf cuttings (yellow-edged 'Laurentii' reverts to plain green from leaf cuttings)	Low light; drought-tolerant	Root rot from overwatering; mealybugs	CAM; West Africa
Snapdragon (Antirrhinum majus)	Plantaginaceae	Herbaceous tender perennial grown as cool-season annual	Ornamental (bedding, cut flower)	Seed (needs light); cuttings	Cool; tolerates light frost	Snapdragon rust (Puccinia antirrhini); botrytis; downy mildew	Zygomorphic two-lipped flowers opened by bumblebees; model for flower development (ABC model) and peloric mutants
Sorghum (Sorghum bicolor)	Poaceae	Grass; warm-season annual	Grain (caryopsis); sweet stalk syrup; forage; broomcorn	Seed	Very drought- and heat-tolerant (waxy bloom, rolls leaves, can go dormant); SD	Sugarcane aphid; anthracnose; head smut; ergot	C4; young or drought-stressed plants contain dhurrin, releasing prussic acid (HCN) that poisons livestock; origin northeastern Africa; Kansas leads U.S.
Soybean (Glycine max)	Fabaceae	Herbaceous; warm-season annual	Seeds (about 20% oil, 40% protein); immature pods as edamame	Seed	SD (cultivars in maturity groups by latitude); self-pollinated	Soybean cyst nematode (top U.S. yield robber); sudden death syndrome; Asian soybean rust; soybean aphid	Most common GM crop (glyphosate-tolerant, 1996); nodules with Bradyrhizobium japonicum; C3; origin northeastern China; U.S. and Brazil lead; tofu, oil, feed
Spider plant (Chlorophytum comosum)	Asparagaceae	Herbaceous monocot perennial with tuberous roots; houseplant	Ornamental (foliage)	Plantlets on stolons; division	Bright indirect light; tolerant	Leaf-tip burn from fluoride and salts; scale	Non-toxic to pets; South Africa
Spinach (Spinacia oleracea)	Amaranthaceae	Herbaceous; cool-season annual	Leaves	Seed, direct-sown in early spring or fall	Frost-hardy; LD, bolts quickly as days lengthen and warm	Downy mildew (blue mold, Peronospora effusa); leaf miners; aphids	Dioecious (some monoecious); oxalates bind calcium and iron; C3; origin Persia
Squash, summer (Cucurbita pepo: zucchini, yellow, pattypan)	Cucurbitaceae	Herbaceous bush or vine; warm-season annual	Immature fruit (pepo), picked at about 6 to 8 in.	Seed after frost	Frost-tender; monoecious (male flowers first); bees; pick every 1 to 2 days	Squash vine borer; squash bug; powdery mildew; cucumber beetles	Flowers are edible; same species as acorn squash and many pumpkins
Squash, winter (Cucurbita maxima, C. moschata, C. pepo)	Cucurbitaceae	Herbaceous vine; warm-season annual	Mature fruit (pepo) with a hard rind	Seed after frost	Long, warm season; harvest mature and cure about 1 to 2 weeks warm before storing	Squash vine borer (butternut, C. moschata, resists it); squash bug; powdery mildew	Butternut (C. moschata), Hubbard (C. maxima), acorn (C. pepo); stores for months
Strawberry (Fragaria × ananassa)	Rosaceae	Herbaceous perennial	Aggregate accessory fruit: enlarged fleshy receptacle with achenes on the surface	Runners (stolons) with daughter plants; tissue culture for clean stock	Full sun; June-bearing (SD), everbearing and day-neutral cultivars; matted rows or annual plasticulture; renovate June-bearers after harvest	Gray mold (Botrytis cinerea); tarnished plant bug; spotted wing drosophila; slugs; Verticillium wilt	Octoploid hybrid of F. virginiana (North America) × F. chiloensis (Chile), made in France in the 1700s; non-climacteric; California grows about 90% of U.S. crop
Sugar beet (Beta vulgaris, Altissima group)	Amaranthaceae	Herbaceous; biennial grown as annual	Storage root (sucrose about 16 to 20%)	Seed (monogerm seed avoids thinning)	Cool, temperate	Cercospora leaf spot; rhizomania (virus spread by a soil protist); beet cyst nematode	Supplies roughly 20% of world sugar; developed in Prussia (1700s) and promoted by Napoleon; most U.S. sugar beets are GM herbicide-tolerant
Sugarcane (Saccharum officinarum and hybrids)	Poaceae	Tall tropical grass; perennial	Stem (culm) juice, sucrose stored in parenchyma	Stem cuttings ("setts") with nodes and buds; ratoon crops regrow from stubble	Tropical and subtropical; frost-tender; long season	Red rot; smut; sugarcane borer; mosaic virus	C4, among the most productive crops; about 80% of world sugar; bagasse burned for fuel; Brazil makes cane ethanol; origin New Guinea
Sunflower (Helianthus annuus)	Asteraceae	Herbaceous; warm-season annual	Fruit (cypsela, the "seed"), for oil and snacks	Seed	Full sun; drought-tolerant with a deep taproot	Sunflower moth; downy mildew; Sclerotinia head rot	Head (capitulum) of ray and disk florets in Fibonacci spirals; young heads track the sun, mature heads face east; allelopathic; native to North America; Kansas state flower
Sweet pea (Lathyrus odoratus)	Fabaceae	Herbaceous tendril vine; cool-season annual	Ornamental (fragrant cut flowers)	Seed (nick or soak)	Cool; sow early; LD	Powdery mildew; aphids	Seeds toxic (lathyrism); Bateson and Punnett discovered gene linkage in sweet pea (1905); not edible like garden pea
Sweet potato (Ipomoea batatas)	Convolvulaceae	Herbaceous vine; perennial grown as warm-season annual	Storage (tuberous) root, a true root	Slips (sprouts grown from bedded roots)	Hot, sandy soil; frost-tender; about 90 to 120 days; cure about 85 °F and high humidity for about a week (heals wounds, sweetens)	Sweet potato weevil; root-knot nematodes; black rot; scurf	Not a true yam; origin Central and South America; North Carolina leads U.S.; its genome naturally carries Agrobacterium DNA
Taro (Colocasia esculenta)	Araceae	Herbaceous monocot; perennial	Corm; leaves cooked	Huli (corm top with leaf-stalk bases); cormels	Tropical; flooded paddies or upland	Taro leaf blight (Phytophthora colocasiae)	Raw tissue has irritating calcium oxalate raphides, so it is always cooked; Hawaiian poi; ornamental "elephant ears"
Tea (Camellia sinensis)	Theaceae	Evergreen shrub kept pruned to a "plucking table"; perennial	Young leaves and buds ("two leaves and a bud")	Cuttings; seed	Acid soil (pH about 4.5 to 5.5); humid subtropics and tropical highlands	Blister blight (Exobasidium vexans); tea mosquito bug; red spider mite	Black tea fully oxidized ("fermented"), oolong partly, green unoxidized (heated quickly); caffeine, theanine, catechins; origin southwestern China; China the top producer
Thyme (Thymus vulgaris)	Lamiaceae	Woody subshrub; perennial	Leaves	Cuttings; layering; division	Full sun; dry, well-drained	Root rot in wet soil	Thymol is antiseptic; Mediterranean
Tobacco (Nicotiana tabacum)	Solanaceae	Herbaceous; annual in culture (perennial in the tropics)	Leaves (cured: flue-, air-, fire- or sun-cured)	Tiny seed, grown as float-bed transplants	Warm; "topping" (removing flowers) and removing suckers send more growth to leaves	Tobacco mosaic virus; blue mold (Peronospora tabacina); black shank; tobacco hornworm	Nicotine is made in the roots and moved to leaves (a natural insecticide); TMV was the first virus discovered; 'Maryland Mammoth' led to the discovery of photoperiodism (1920); among the first transgenic plants; origin South America
Tomatillo (Physalis philadelphica)	Solanaceae	Herbaceous; warm-season annual	Fruit (berry) inside an inflated papery calyx (husk)	Seed, transplanted	Frost-tender; self-incompatible, so plant at least two	Flea beetles; Colorado potato beetle	Salsa verde; origin Mexico
Tomato (Solanum lycopersicum)	Solanaceae	Herbaceous perennial grown as warm-season annual; determinate (bush) or indeterminate (vine)	Fruit (berry); legally a vegetable (U.S. Supreme Court, 1893)	Seed, started indoors and transplanted deep (stems form adventitious roots); suckers root as cuttings; grafted onto resistant rootstocks	Frost-tender; full sun; self-pollinating (vibration helps); fruit set fails with hot days above about 90 °F, nights above about 72 °F or nights below about 55 °F; stake or cage	Blossom-end rot (calcium, uneven watering); early blight (Alternaria); late blight; Septoria leaf spot; Fusarium and Verticillium wilts ("VFN" resistance codes); hornworms	DN; C3; climacteric (ethylene ripening); Flavr Savr (1994) was the first commercial GM food; avoid planting near black walnut (juglone) or potatoes; leaves contain tomatine; origin Andes, domesticated in Mexico
Tulip (Tulipa hybrids)	Liliaceae	Monocot bulb (tunicate); perennial, often treated as annual	Ornamental (spring flowers; cut flower)	Offset bulbs; seed takes years to bloom	Plant in fall 6 to 8 in. deep; needs about 12 to 16 weeks of cold (pre-chilled bulbs in the South)	Tulip breaking virus (aphids); tulip fire (Botrytis tulipae); squirrels and deer	Virus-striped "broken" tulips fueled Dutch tulip mania (1630s); origin Central Asia and Turkey; Netherlands leads production; blooms in early spring
Turmeric (Curcuma longa)	Zingiberaceae	Herbaceous monocot; perennial	Rhizome (yellow curcumin)	Rhizome pieces (seldom sets seed)	Hot, humid tropics; part shade	Rhizome rot; leaf blotch	India grows most of the world's crop; ginger family
Turnip (Brassica rapa, Rapifera group)	Brassicaceae	Herbaceous; biennial grown as cool-season annual	Storage organ (swollen hypocotyl and taproot); leaves (greens)	Seed	Cool-season; spring or fall	Cabbage root maggot; flea beetles; clubroot	Same species as Napa cabbage and bok choy
Vanilla (Vanilla planifolia)	Orchidaceae	Climbing epiphytic monocot vine; perennial	Cured fruit (capsule, the "bean")	Stem cuttings	Humid tropics; partial shade; support trees	Fusarium root and stem rot	Flowers are hand-pollinated (method found by Edmond Albius, Réunion, 1841); curing forms vanillin; native to Mexico; Madagascar grows most; CAM
Walnut (Juglans regia, English or Persian; J. nigra, black)	Juglandaceae	Deciduous tree; perennial	Seed of a drupe-like nut (hard shell inside a green husk); black walnut timber	Grafted onto black walnut or 'Paradox' hybrid rootstock	Full sun; monoecious, wind-pollinated (male and female flowers mature at different times)	Walnut blight (Xanthomonas); codling moth; walnut husk fly; thousand cankers disease (black walnut)	Roots and husks release juglone, which harms tomatoes, potatoes, apples and azaleas (allelopathy); California grows nearly all U.S. English walnuts
Watermelon (Citrullus lanatus)	Cucurbitaceae	Herbaceous vine; warm-season annual	Fruit (pepo)	Seed or transplants; grafted onto gourd or squash rootstocks to resist soil disease	Long, hot season; sandy soil; monoecious, bees; ripe when the ground spot turns yellow and the nearest tendril dries	Fusarium wilt; anthracnose; gummy stem blight; cucumber beetles	Seedless types are triploid (tetraploid × diploid) and need diploid pollinizer rows; non-climacteric; lycopene; origin northeastern Africa
Wheat (Triticum aestivum, bread; T. turgidum subsp. durum, pasta)	Poaceae	Grass; cool-season annual (winter wheat needs vernalization; spring wheat does not)	Grain (caryopsis, "wheat berry"); flour is ground endosperm	Seed (drilled)	Winter wheat sown in fall, harvested early summer; LD; self-pollinating	Stem rust (Puccinia graminis, alternate host barberry; race Ug99); leaf and stripe rusts; Fusarium head blight (scab); Hessian fly	Bread wheat is hexaploid, durum tetraploid; C3; gluten proteins (gliadin, glutenin) in the endosperm; Borlaug's semi-dwarf cultivars drove the Green Revolution; domesticated in the Fertile Crescent; Kansas (winter wheat) and North Dakota (spring and durum) lead U.S.
Willow (Salix alba, white; S. babylonica, weeping; others)	Salicaceae	Deciduous tree or shrub; perennial	Bark (salicin, the model for aspirin); flexible stems (wicker, osier); biomass	Hardwood cuttings (root very easily, even stuck in wet soil)	Wet soils, full sun; fast-growing	Willow scab; cankers; aphids	Dioecious catkins; "willow water" is a traditional homemade rooting aid
Wisteria (Wisteria sinensis, Chinese; W. floribunda, Japanese; W. frutescens, American)	Fabaceae	Deciduous woody twining vine; perennial	Ornamental (hanging flower clusters, racemes)	Grafting; layering; cuttings (seedlings may take many years to flower)	Full sun; avoid high-N fertilizer; prune in summer and winter	Few serious pests; scale	Asian species invasive in the Southeast; seeds and pods toxic
Yam (Dioscorea rotundata, D. alata and others)	Dioscoreaceae	Herbaceous monocot vine; perennial	Tuber	Setts (tuber pieces); minisetts	Tropical; staking	Yam mosaic virus; nematodes; anthracnose	West Africa (Nigeria) grows most of the world's yams; wild Mexican yams supplied diosgenin to make steroid hormones (birth control pill); U.S. "yams" are sweet potatoes
Yew (Taxus baccata, English; T. brevifolia, Pacific; T. × media)	Taxaceae	Evergreen conifer shrub or tree; perennial	Ornamental hedges; bark and needles yield paclitaxel (Taxol)	Cuttings; seed	Shade-tolerant; needs good drainage	Root rot in wet soil; taxus weevil	Seeds sit in a red fleshy aril; the aril is the only non-toxic part (taxine alkaloids); paclitaxel treats ovarian and breast cancer; dioecious
Zinnia (Zinnia elegans)	Asteraceae	Herbaceous; warm-season annual	Ornamental (flower heads; cut flower)	Seed, direct-sown (easy)	Full sun; heat-loving; frost-tender	Powdery mildew; Alternaria and bacterial leaf spots	Origin Mexico; first flowering plant grown in NASA's Veggie unit on the International Space Station (2016)

Genetically modified organisms

A GMO carries DNA changed with genetic engineering rather than by crossing alone; a plant carrying a gene from another species is transgenic. Genetic engineering can make targeted changes in a few years that traditional breeding might take decades to achieve, and it can move genes between unrelated species (bacterial genes into plants, for example).

Agrobacterium-mediated transformation. Agrobacterium tumefaciens, the soil bacterium that causes crown gall, naturally inserts a piece of its Ti (tumor-inducing) plasmid, a large circle of DNA separate from the bacterial chromosome, into plant chromosomes. That transferred DNA (T-DNA) carries genes that make the plant cells overproduce auxin and cytokinin (so they grow into a tumor) and make opines, unusual compounds built from amino acids plus keto acids or sugars that only the bacterium can use as food. The plasmid's vir (virulence) genes do the cutting and transfer. Engineers "disarm" the plasmid by removing the tumor and opine genes and put in the gene of interest (with a promoter that controls where it is expressed) plus a selectable marker (an antibiotic- or herbicide-resistance gene) so transformed cells can be picked out. Transformed cells are regenerated into whole plants by tissue culture. Limits: it works best on dicots and some species resist infection, the T-DNA lands at random sites in the genome (which can disrupt or alter the expression of the plant's own genes), and tissue culture can introduce unwanted mutations. The vir genes are switched on by phenolic compounds such as acetosyringone that leak from wounded plant cells, which is why wounding (or adding acetosyringone) starts transformation.

Biolistics (the gene gun) fires microscopic (about 1 µm) gold or tungsten particles coated with the DNA of interest into plant cells. It works on almost any species, including grasses and even chloroplast genomes, but it damages tissue and often inserts many broken copies at random sites. Restriction enzymes cut DNA at specific sequences and DNA ligase joins fragments; PCR copies DNA. Newer gene editing (CRISPR-Cas9) makes targeted changes to a plant's own genes, often without adding foreign DNA, and RNA interference silences a gene.

Bt proteins are made as inactive crystals; in the alkaline gut of a susceptible insect they are activated, bind receptors in the midgut lining and punch pores that kill the insect. Each Cry protein targets a group: Cry1 proteins kill caterpillars (Lepidoptera, such as the European corn borer and cotton bollworm), Cry3 proteins kill beetles (Colorado potato beetle, corn rootworm). Mammals have an acidic stomach and lack the receptors. Insects evolve resistance (often through mutations in those midgut receptors), so growers plant non-Bt refuges that keep susceptible insects in the population. In 1999 a Cornell laboratory study reported that Bt corn pollen dusted on milkweed harmed monarch caterpillars, setting off the "Bt corn controversy"; later field studies found the real-world risk to monarchs was low.

Glyphosate (Roundup) kills plants by blocking EPSPS, an enzyme of the shikimate pathway that plants (but not animals) use to make aromatic amino acids. Herbicides are selective (kill some plants and spare others: 2,4-D and MCPA, synthetic auxins that kill broadleaf weeds in grass crops; atrazine, a photosystem II blocker that corn tolerates) or nonselective (kill nearly all green plants: glyphosate; paraquat, which steals electrons from photosystem I).

Regulation in the United States is shared: the USDA (APHIS) regulates GM plants as potential plant pests, the EPA regulates pesticidal traits such as Bt proteins and herbicide use, and the FDA reviews food safety. The Supreme Court case Diamond v. Chakrabarty (1980) held that a genetically engineered bacterium, a living organism made by people, can be patented (later cases extended this to plants). Soybeans are the most widely grown GM crop worldwide; corn, cotton and canola follow. Large-scale U.S. planting began in 1996 with Bt corn and Roundup Ready soybeans (Bt potatoes and cotton arrived about the same time), and adoption was fast: today more than 90% of U.S. corn, soybean and cotton acreage is genetically engineered. By crop, roughly 95% of soybean and cotton acreage and over 90% of corn acreage are GE (mostly herbicide-tolerant, insect-resistant or both). Most GM crops carry only one or a few added genes, often "stacked" traits combined by crossing. The first wave of GM foods reaching U.S. shoppers included corn, soybeans, papaya, tomatoes, potatoes and squash. GM varieties grown commercially in the United States today include corn, soybeans, cotton, canola, sugar beets, alfalfa, papaya, summer squash, potatoes and apples; there are no GM avocados, and tomatoes are essentially absent from GM production (the Flavr Savr was withdrawn in the 1990s; a purple, anthocyanin-rich GM tomato went on sale in 2024 only on a small scale). The FDA completed its safety consultation on Golden Rice in 2018, and the Philippines approved it for planting in 2021 (a 2024 court order there halted commercial planting); a 2008 feeding trial on children in China drew heavy criticism over consent. Thousands of studies have examined the safety of GM crops, and major scientific bodies have found approved GM foods as safe to eat as their conventional counterparts. Plants are also engineered as factories (molecular farming): the first pharmaceutical proteins made in transgenic plants (a human growth hormone fusion in tobacco in 1986 and human serum albumin in 1990) were followed by commercial products such as avidin from corn and an enzyme drug for Gaucher disease made in carrot cells, approved in 2012.

Because most corn, soybeans, canola and sugar beets grown in the U.S. are GM, ingredients derived from them (corn syrup, soybean oil and lecithin, canola oil, beet sugar) are in an estimated 70 to 80% of U.S. packaged foods; since 2022 U.S. law requires a "bioengineered" disclosure on qualifying foods. The common concerns are pest and weed resistance (insects evolving tolerance to Bt, glyphosate-resistant weeds), gene flow (transgenes can and do escape into wild or weedy relatives by cross-pollination), effects on non-target organisms, unintended changes from random insertion, labeling, and corporate control and patenting of seed. The benefits claimed are higher yields, less insecticide spraying, easier no-till weed control, virus resistance, better nutrition and less food waste. Tests often ask for one benefit and one risk, so prepare both.

Plant diseases and nutrient deficiencies

Infections

Disease needs three things together, the disease triangle: a susceptible host, a virulent pathogen and a favorable environment (often warm, wet weather or crowded, poorly ventilated plants). Remove any one and the disease stops, which is the logic behind most control methods (resistant varieties, sanitation, crop rotation, adjusting watering and spacing). Biotic (infectious) diseases are caused by living pathogens; abiotic disorders by the environment: nutrient deficiencies or excesses, drought, flooding, extreme heat or cold (frost, sunscald), salt, air pollution, herbicide drift and mechanical injury.

To prove that a microbe causes a plant disease, pathologists follow Koch's postulates: (1) the microbe is found in every diseased plant; (2) it is isolated and grown in pure culture; (3) the pure culture, inoculated into a healthy plant, causes the same disease; (4) the same microbe is re-isolated from that plant. Obligate parasites such as rusts, powdery mildews and viruses cannot be grown in pure culture, so the postulates are adapted for them.

To tell them apart in the field: biotic diseases usually affect one host species or family, start in patches and spread over days to weeks, and may show signs, the pathogen itself (fungal threads or spores, bacterial ooze, nematode cysts, mushroom-like fruiting bodies). Abiotic problems tend to appear suddenly across a whole area or across many species at once, in a uniform pattern linked to an event (a frost, a spill, a drought), and do not spread from plant to plant. Symptoms are the plant's responses; signs are the pathogen.

ReferencePlant diseases to know· 31 rows

31 rows

Disease	Cause	What to know
Late blight of potato and tomato	Oomycete, Phytophthora infestans	Caused the Irish potato famine (1845-1849); dark, water-soaked lesions; not a true fungus
Damping-off	Pythium, Rhizoctonia and other soil organisms	Seedlings rot at the soil line and topple; prevent with sterile mix, drainage and not overwatering
Downy mildew	Oomycetes	Yellow patches on top of leaves with fuzzy gray-purple growth underneath, in cool wet weather
Powdery mildew	Fungi	White powdery coating on leaf surfaces; favored by humid nights and dry leaves, crowding and shade
Anthracnose	Fungi (Colletotrichum and others)	Dark, sunken lesions on leaves, stems and fruit
Black stem rust of wheat	Fungus, Puccinia graminis (kingdom Fungi, order Pucciniales)	Rust-red pustules; its alternate host is barberry; the strain Ug99 threatens wheat worldwide
Coffee leaf rust	Fungus, Hemileia vastatrix	Devastated Central and South American coffee in an epidemic that began in 2012
White pine blister rust	Fungus	Alternates between five-needle pines and currants and gooseberries (Ribes), which were once banned in many states
Corn smut	Fungus, Ustilago maydis	Swollen gray galls full of black spores on ears; eaten as huitlacoche in Mexico
Ergot	Fungus, Claviceps purpurea	Hard dark sclerotia replace rye grains; its alkaloids cause ergotism (St. Anthony's fire) and are the starting point for LSD
Dutch elm disease	Fungus spread by elm bark beetles	The fungus clogs xylem, so the crown wilts; managed by sanitation (pruning out and burning infected wood), breaking root grafts, fungicide injections and resistant elms
Chestnut blight	Fungus, Cryphonectria parasitica	Cankers girdled and wiped out the American chestnut as a canopy tree after its arrival around 1904
Oak wilt; sudden oak death	Fungus spread by sap beetles and root grafts; oomycete Phytophthora ramorum	Kill oaks; red oaks die fastest
Fusarium and Verticillium wilts	Soil fungi	Invade roots and plug xylem; attack tomatoes, potatoes, peppers, eggplant, brambles and many others; survive in soil for years, so rotate away from susceptible crops for several years
Panama disease of banana	Fungus, Fusarium oxysporum f. sp. cubense	Wiped out the Gros Michel banana; a new strain (TR4) threatens the clonal Cavendish
Clubroot	Plasmodiophora brassicae (a protist)	Swollen, distorted roots of cabbage-family crops; favored by acidic soil, controlled by liming
Apple scab; brown rot	Fungi	Corky olive spots on apples; brown rot mummifies stone fruits
Fire blight	Bacterium, Erwinia amylovora	Apples and pears: shoots look scorched and curl into a "shepherd's crook"; spread by bees and rain; prune well below cankers and disinfect tools. Native to North America (first reported in New York's Hudson Valley in 1780); Thomas Burrill showed in the 1870s-1880s that a bacterium causes it, the first plant disease proven to be bacterial
Bacterial canker of stone fruits	Bacterium, Pseudomonas syringae	Sunken, oozing, gummy cankers on cherry, plum and peach
Crown gall	Bacterium, Agrobacterium tumefaciens	Tumor-like galls at the soil line; the same bacterium is used to make GMOs
Bacterial wilt of cucurbits	Bacterium spread by cucumber beetles	Sudden wilting of cucumbers and melons
Pierce's disease of grapes	Bacterium, Xylella fastidiosa, spread by sharpshooter leafhoppers	Clogs the xylem, scorching leaves and killing vines; the same bacterium kills olive trees in Italy
Citrus greening (huanglongbing)	Phloem bacterium spread by the Asian citrus psyllid	The most destructive citrus disease; lopsided, bitter fruit
Tobacco mosaic virus	Virus	Mottled light and dark leaves; the first virus ever identified (1890s); spread by touch, tools and even tobacco products
Tomato spotted wilt; cucumber mosaic	Viruses	Spread by thrips and aphids respectively
Tomato yellow leaf curl	A geminivirus (a DNA virus) spread by the whitefly Bemisia tabaci	Yellow, upcurled, crumpled leaves and stunted, barren plants
Bacterial soft rot	Pectobacterium carotovorum (formerly Erwinia carotovora)	Enzymes dissolve pectin, turning potatoes, carrots and other fleshy organs into foul-smelling mush
Papaya ringspot	Virus spread by aphids	Controlled by GM Rainbow papaya
Beech leaf disease	A foliar nematode	First found in northeastern Ohio in 2012; dark bands between leaf veins; spreading through the northeastern U.S. and Ontario
Southern corn leaf blight (1970)	Fungus	Swept through U.S. corn that shared the susceptible Texas male-sterile cytoplasm
Root-knot nematode	Nematodes (Meloidogyne)	Swollen galls on roots of tomatoes, peppers and many crops; stunting and wilting; marigolds suppress them

Plant virus families tests name: Potyviridae (the largest family of plant RNA viruses; potato virus Y, papaya ringspot, turnip mosaic; aphid-borne), Bromoviridae (cucumber mosaic, alfalfa mosaic), Virgaviridae (tobacco mosaic), Geminiviridae (DNA viruses carried by whiteflies and leafhoppers) and Tospoviridae (tomato spotted wilt, carried by thrips). Insect pests matter twice, as direct damage and as vectors. By feeding style: defoliators chew leaves (caterpillars such as hornworms and spongy moth larvae, Japanese beetles), borers tunnel into stems and wood (emerald ash borer, squash vine borer, bark beetles), leaf miners tunnel between the upper and lower leaf surfaces, root feeders attack roots (grubs, corn rootworm), and sap-suckers pierce and drink (aphids, whiteflies, scale, leafhoppers, psyllids). Thrips rasp leaf and petal surfaces and suck the contents, leaving silvery or white stippled patches dotted with tiny black fecal specks (and they spread tomato spotted wilt virus). Scale insects are among the hardest pests to control because adults hide under a waxy or armored shell that sprays cannot penetrate; the crawling young are the vulnerable stage. Whiteflies swarm from the undersides of tobacco, tomato and greenhouse plants. Spider mites are tiny arachnids, not insects; they hide under leaves and cause stippled, yellowing, curling leaves with fine webbing in hot, dry weather. By sucking out leaf cells they cut photosynthesis, and heavy infestations cause leaf drop and smaller crops the next year in orchards such as almonds. Tomatoes alone host aphids, whiteflies, spider mites, mealybugs (in greenhouses), thrips, hornworms, fruitworms and flea beetles. The potato leafhopper feeds on potatoes, beans and alfalfa; its toxic saliva causes hopperburn, a V-shaped yellowing and then browning that starts at leaf tips. The Colorado potato beetle strips the foliage of nightshade-family crops, especially potatoes and eggplants, and also tomatoes and sometimes peppers.

How plants defend themselves. Preformed barriers come first: cuticle, bark, cell walls and antimicrobial chemicals. Plants then recognize pathogens in two layers. Pattern-triggered immunity (PTI) uses surface receptors for common microbial molecules such as bacterial flagellin or fungal chitin; effector-triggered immunity (ETI) uses resistance (R) proteins that recognize a specific pathogen effector, giving strong, race-specific resistance (the gene-for-gene model) that often ends in the hypersensitive response. Defenses include the hypersensitive response (cells around the infection site kill themselves, walling the pathogen off in a small dead spot), phytoalexins (antimicrobial compounds made after infection), pathogenesis-related proteins (chitinases and glucanases that attack fungal walls), wall fortification with callose and lignin, tyloses and gums that plug infected xylem, and RNA silencing against viruses. Salicylic acid then spreads a signal that primes the whole plant (systemic acquired resistance), while jasmonic acid and ethylene coordinate defenses against chewing insects and rotting pathogens. Trees compartmentalize decay behind chemical and anatomical walls instead of healing it. Some resistance comes from losing a gene the pathogen needs: recessive mlo mutations give barley (and other crops) broad, durable resistance to powdery mildew.

Control combines cultural methods (resistant varieties, crop rotation, sanitation and removal of infected material, removing alternate hosts, spacing for airflow, watering the soil rather than the leaves, disinfecting tools), chemical controls (fungicides such as copper sprays and the Bordeaux mixture first used on grape downy mildew in the 1880s, bactericides, insecticides against vectors), biological controls, quarantines against introduced pathogens, and integrated pest management (see Horticulture). Rotations against soil diseases and insects need to keep susceptible crops (and their relatives) out of a field for about three or four years. Wiping powdery mildew off a leaf does not cure it, because the fungus keeps growing and sporulating; it needs pruning for airflow, resistant cultivars or a fungicide. Plants can even be "vaccinated": spraying chemicals that switch on systemic acquired resistance, or pre-infecting with a mild virus strain (cross-protection, used against citrus tristeza and papaya ringspot), gives protection against later infection.

Nutrient deficiencies

Plants need 17 essential elements. An element is essential if the plant cannot complete its life cycle without it, no other element can replace it, and it acts directly in the plant's metabolism. The standard test grows plants in hydroponic solution culture: one group gets a complete nutrient solution and another an identical solution missing the element, and everything else is held constant. Carbon, hydrogen and oxygen come from air and water and make up about 95% of dry mass (oxygen and carbon are each roughly 45%, hydrogen about 6%). The rest come from the soil:

• Primary macronutrients: nitrogen (N), phosphorus (P) and potassium (K), the three numbers on a fertilizer bag; nitrogen is needed in the largest amount.
• Secondary macronutrients: calcium (Ca), magnesium (Mg) and sulfur (S).
• Micronutrients (needed in trace amounts): iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl) and nickel (Ni).

The key to diagnosing a deficiency is mobility. A plant can move mobile nutrients out of old leaves into new growth, so a shortage shows in the older, lower leaves first. Immobile nutrients stay where they were first deposited, so a shortage shows in the youngest leaves and growing tips. Chlorosis that appears only on the lower leaves therefore points to a mobile nutrient.

ReferenceNutrient roles and deficiency symptoms· 14 rows

14 rows

Nutrient	Mobility	Main role	Deficiency symptoms
Nitrogen (N)	Mobile	Amino acids and proteins, nucleic acids, chlorophyll	Uniform yellowing of older leaves while upper leaves stay green; stunting; spindly growth
Phosphorus (P)	Mobile	ATP, DNA and RNA backbone, phospholipid membranes	Dark green leaves with purple or reddish tints (anthocyanin buildup), especially older leaves and stems; poor roots, flowering and fruiting; delayed maturity
Potassium (K)	Mobile	Guard-cell turgor and stomatal control, enzyme activation, water balance	Scorched, browning edges (marginal necrosis) on older leaves; weak stalks that fall over (lodging); poor roots; poor disease resistance
Magnesium (Mg)	Mobile	Center of the chlorophyll molecule; activates enzymes, including RuBisCO	Yellowing between the veins of older leaves, veins stay green
Calcium (Ca)	Immobile	Cell walls (calcium pectate in the middle lamella), membranes, signaling	Dead growing tips; blossom-end rot of tomatoes and peppers; tipburn of lettuce; bitter pit of apples
Sulfur (S)	Mostly immobile	Amino acids (cysteine, methionine), coenzymes	Uniform yellowing of young leaves
Iron (Fe)	Immobile	Chlorophyll synthesis, cytochromes and ferredoxin	Yellowing between the veins of young leaves, which can turn almost white; common in alkaline soil
Manganese (Mn)	Immobile	Water-splitting complex of photosystem II; enzymes	Interveinal chlorosis of young leaves, sometimes with small dead spots
Zinc (Zn)	Immobile	Enzymes; needed to make tryptophan, the precursor of auxin	Small, narrow leaves ("little leaf"), short internodes and rosettes; delayed spring growth with small, chlorotic terminal buds; in corn, broad white or yellow bands on each side of the midrib of young leaves ("white bud")
Copper (Cu)	Immobile	Plastocyanin (photosynthesis), cytochrome c oxidase (respiration), enzymes that build lignin and that detoxify oxygen radicals (Cu/Zn superoxide dismutase)	Young leaves dark, twisted or wilted; dieback of tips
Boron (B)	Immobile	Cell walls (cross-links pectin), cell division, sugar transport, pollen tube growth; linked to calcium use and water uptake	Death of terminal buds; brittle, distorted, cracked new growth; hollow or corky stems and roots; poor fruit set
Molybdenum (Mo)	Mobile	Nitrogenase and nitrate reductase	Looks like nitrogen deficiency; "whiptail" leaves in cauliflower
Chlorine (Cl)	Mobile	Water splitting, osmotic balance	Wilting, bronzing (rare in the field)
Nickel (Ni)	Mobile	Urease (breaks down urea)	Necrotic leaf tips from urea buildup; "mouse-ear" leaves in pecans

Symptoms look a little different crop by crop. In corn, nitrogen deficiency yellows older leaves in a V running from the tip down the midrib, potassium deficiency browns the leaf margins of older leaves, and zinc deficiency makes pale bands on young leaves. In citrus, magnesium deficiency gives older leaves a yellow band with a green, inverted-V wedge at the base, zinc deficiency gives small, mottled young leaves, and iron deficiency gives yellow young leaves with green veins. Acid-loving blueberries, azaleas and pin oaks show iron chlorosis whenever the soil is too alkaline.

Soil pH controls availability: most nutrients are easiest to absorb in slightly acidic to neutral soil (about pH 6 to 7). Iron, manganese, zinc and phosphorus become scarce in alkaline soil, so before adding iron to a chlorotic plant, test the pH: if it is high, the iron already in the soil cannot be absorbed. Fix iron chlorosis by lowering the pH (sulfur, acidifying fertilizer) or applying chelated iron to the soil or as a foliar spray. In very acidic soil, aluminum and manganese become soluble and toxic and calcium, magnesium and molybdenum become scarce. Too much fertilizer is its own disorder: salt buildup pulls water out of roots and burns leaf margins.

Division C topics

Horticulture and aquaculture

Horticulture (Latin hortus, garden, + cultura, cultivation) is the science and art of growing fruits, vegetables, flowers and ornamental plants, usually intensively and on a small area per plant. Agronomy covers field crops grown over large areas (wheat, corn, soybeans, forage), and forestry covers trees grown in stands. It is one of the larger topics in past Botany tests, and most of it is practical: name the branch, pick the propagation method, do the fertilizer arithmetic, explain why a gardening practice works. The physiology behind almost every answer is in the earlier sections of this guide (apical dominance, adventitious roots, photoperiod, vernalization, nutrient mobility).

Branches of horticulture

Two neighboring words are not horticulture: silviculture is growing forest trees as stands for timber and other wood products (forestry), and apiculture is beekeeping. Phenology is the study of seasonal timing in living things (first bloom, leaf-out, bird migration), which horticulturists use to time planting and pest control. Ornamental horticulture includes indoor plants as well as outdoor landscapes. Landscape design combines softscape (plants, turf) with hardscape (paths, walls, patios) and garden structures: a trellis is a flat frame or lattice that supports climbing plants; an arbor is a freestanding arched or roofed frame, often over a path or gate; a pergola is a larger structure of posts carrying an open roof of beams that vines can cover; a gazebo is a roofed, open-sided pavilion. The rose is the most popular cut flower in the United States, and the poinsettia (forced into color with long nights, see Light, day length and timing) is the best-selling potted flowering plant.

Propagation

Sexual propagation is growing from seed. Seed is cheap and carries genetic variation, but many cultivars (named, selected varieties) do not "come true" from seed: an apple seed grows into a new, unpredictable apple tree. Open-pollinated cultivars, including heirlooms, breed true when pollinated within the cultivar; F₁ hybrids come from crossing two inbred parents every year, so saved seed from them segregates and does not match the parent.

Asexual (vegetative) propagation produces clones, genetically identical to the parent, because only mitosis is involved. It works because many plant cells stay totipotent and meristematic tissue can form new organs. The main methods:

Micropropagation must be done under aseptic (sterile) conditions, because the sugary medium grows bacteria and fungi far faster than plant cells. It runs in stages: establish a clean explant, multiply shoots (high cytokinin-to-auxin ratio), root them (more auxin), then acclimatize the plantlets to open air ("hardening"). One explant can yield thousands of identical plants. Culture types include shoot-tip and meristem culture (meristems are often virus-free, so this "cleans up" infected stock), callus culture (an undifferentiated cell mass), embryo culture, anther culture (haploid plants) and cell-suspension culture. For citrus, viruses are eliminated by shoot-tip micrografting: a tiny shoot tip (well under a millimeter) from an infected tree is grafted onto a seedling rootstock grown in a test tube, giving virus-free budwood.

Grafting joins the scion (the upper part, which carries the desired cultivar and becomes the whole shoot system) to the rootstock (the root system and lower stem). The one essential requirement is cambium-to-cambium contact: the vascular cambium of both pieces must line up so that new xylem and phloem can knit across the union. Grafts take only between closely related plants, usually within a genus or family (a tomato scion on a potato rootstock works because both are Solanum, giving tomatoes above ground and potatoes below). Occasionally grafts work between genera: pears are dwarfed by grafting onto quince rootstock. The desired fruit genes are in the scion; the rootstock is chosen for root traits. Apples, pears, peaches, citrus and roses are propagated commercially by grafting or budding cultivars onto rootstocks, not from seed.

Why graft? To clone cultivars that do not come true from seed or root poorly from cuttings; to use dwarfing rootstocks that control tree height and bring trees into bearing sooner (apples on Malling series stocks such as M.9); to get rootstock disease and pest resistance (European wine grapes, Vitis vinifera, are grafted onto American Vitis rootstocks such as V. riparia that tolerate the root louse phylloxera; cucumbers and melons are grafted onto nematode- and wilt-resistant cucurbit stocks); to suit a rootstock to drought or soil; to put several cultivars or species on one tree (multi-grafted "fruit salad" trees); to insert an interstem between rootstock and scion (double working, also called intergrafting); and to repair damage. A grafted grapevine usually needs about three years to bear a crop worth harvesting. Good grafting stock is disease- and virus-free and true to name; the rootstock is chosen for the local climate, soil and pests. Scion wood is usually one-year-old, pencil-thick shoots with plump buds, cut while dormant in winter and kept cool and moist until grafting. Many classic wine-grape vineyards decline in vigor and yield after a few decades (around 20 to 25 years is often quoted) and are replanted.

Pruning and training

Pruning works through apical dominance: the shoot tip makes auxin that keeps the buds below it dormant.

• Pinching removes the terminal bud or tip of a young shoot with the fingers. Side buds are released, so the plant becomes bushier and more compact with more flowering stems (mums, basil, coleus, petunias).
• A heading cut shortens a shoot to a bud and makes the plant denser below the cut. A thinning cut removes a whole branch back to its point of origin and opens the canopy without stimulating a flush of shoots.
• Deadheading removes spent flowers. The plant stops putting resources into seed, which encourages more blooms and keeps it tidy.
• Cut just outside the branch collar (the swollen ring where a branch joins the trunk), never flush. Trees do not heal wounds; they compartmentalize them (Alex Shigo's CODIT model), and the collar holds the tissue that seals the cut off. Wound dressings and paints are not recommended: they do not stop decay and can trap moisture.
• Topping (cutting large branches back to stubs) is never acceptable arboriculture: it starves the tree, invites decay and produces weakly attached sprouts.
• A common pruning dose guideline is to remove no more than about 25% of the live foliage of a mature tree in one season, and less from old or stressed trees. Large wounds and heavy live-tissue removal lead to decay, defects and stress.
• Codominant leaders (two stems of similar size from one point) form a weak V-shaped union with included bark that can split in storms. Structural pruning picks one dominant leader and subordinates or removes the competitor while the tree is young.
• A leader is the main vertical stem; a sucker is a vigorous shoot from the roots or from below a graft union; a water sprout is a vigorous upright shoot from a trunk or branch. Remove both suckers and water sprouts.
• Arboricultural pruning types: crown cleaning (removing dead, diseased and broken branches), crown thinning (selectively removing live branches to let light and wind through), crown raising (removing lower limbs for clearance) and crown reduction (shortening the crown back to lateral branches, the acceptable alternative to topping).
• Tools: hand pruners (bypass pruners, whose blades pass like scissors and make clean cuts on live wood, and anvil pruners, which crush and suit dead wood) for stems up to about 3/4 inch; loppers (long-handled) for thicker branches; pruning saws and pole pruners for large or high limbs; hedge shears for formal hedges. Larger limbs are removed with a three-cut method (an undercut, a top cut farther out to drop the weight, then the final cut at the collar) so the bark does not tear.
• Disinfect pruners between plants (70% alcohol or a dilute bleach solution) so you do not carry diseases such as fire blight from plant to plant.

Timing follows where flowers form. Most fruit trees are pruned while dormant in late winter. Spring-flowering shrubs (forsythia, lilac) bloom on last year's wood, so prune them right after they flower; summer bloomers that flower on new wood are pruned in late winter. Fruit habit matters too: peaches fruit only on one-year-old shoots and are pruned hard every year; apricots fruit on one-year-old shoots and short-lived spurs; apples and pears fruit mainly on long-lived spurs on older wood, so heavy pruning removes crop. Raspberry and blackberry canes are biennial: first-year canes are primocanes and second-year canes are floricanes. Summer-bearing (floricane-fruiting) types fruit on the second-year canes, which then die, so cut them out right after harvest; fall-bearing (primocane-fruiting, everbearing) types also fruit at the tips of first-year canes and can be mowed to the ground each winter. Plums and cherries are best pruned in spring or summer rather than winter, because winter wounds let in silver leaf and bacterial canker; and whenever a plum is pruned, the concern is not to remove too much of the young (one- and two-year-old) wood and spurs that carry the next crops.

Training systems. Apples and pears are usually trained to a central leader (one main trunk, a Christmas-tree outline). Peaches and plums are trained to an open center (vase), which lets sunlight and air into the middle of the tree for better fruit color and less disease. Espalier trains a tree or shrub flat against a wall or trellis; topiary clips shrubs into ornamental shapes; bonsai is the Japanese art of keeping trees miniature in containers by root and shoot pruning; coppicing cuts trees to the ground to regrow many stems, and pollarding does the same at head height. Grapevines are trellised to support the vine and manage the canopy: vertical shoot positioning (VSP) trains shoots upward between wires and suits low- to moderate-vigor vineyards; Scott Henry and Smart-Dyson systems split vigorous canopies into upward and downward curtains (Smart-Dyson alternates upward and downward shoots from the same cordon); bush (goblet) vines are free-standing and traditional in warm, dry regions; the California sprawl lets shoots flop over a single wire, which shades the fruit zone and can cause uneven ripening.

Fruit thinning removes some young fruits soon after bloom. The remaining fruits grow larger and better colored, limbs are less likely to break, and the tree is less likely to fall into biennial bearing (a heavy crop one year, almost none the next).

Soil, media and amendments

Soil texture is the proportion of sand, silt and clay; loam has a balanced mix and is the gardener's ideal. Clay holds water and nutrients but drains and aerates poorly; sand drains fast and holds little. Adding organic matter (compost, manure, leaf mold) improves almost every soil: it binds sand, opens clay, feeds soil organisms and holds nutrients. An ideal garden soil is, by volume, roughly 45% mineral particles, 5% organic matter and 50% pore space, with the pores about half filled with water and half with air. Compaction (from foot traffic, machinery or working wet soil) does the opposite, so "increasing compaction" never improves a garden. Tilling or plowing loosens soil, buries residue and weeds and makes a seedbed, but repeated tillage breaks down structure and organic matter, so no-till and conservation tillage protect soil. Field capacity is the water a soil holds after excess has drained away; the permanent wilting point is the soil moisture below which plants can no longer extract water.

Most vegetables grow best at about pH 6.0 to 7.0 (some guides say 5.5 to 7.0). Acid-loving plants include blueberries (about pH 4.5 to 5.5), azaleas, rhododendrons and camellias; cabbage-family crops such as cauliflower do poorly in strongly acidic soil, where clubroot also thrives. In alkaline soil, iron and manganese become unavailable and acid-lovers turn yellow between the veins (iron chlorosis). Very acidic soil (below about pH 5) releases toxic aluminum ions (Al³⁺) that stunt root elongation, which is why breeders select aluminum-tolerant rice, maize and wheat.

Mulch is any material spread on the soil surface: organic (shredded bark, wood chips, straw, leaves) or inorganic (gravel, plastic sheeting). Landscape fabric (woven or spun weed-barrier cloth laid under rock or bark) is an inorganic mulch that blocks weeds but lets water and air through. It suppresses weeds, conserves soil moisture, moderates soil temperature and, if organic, adds organic matter as it breaks down. Keep it a few inches deep and pulled back from trunks: deep "volcano" mulch against the bark invites rot and pests. Grasscycling is leaving lawn clippings on the lawn to return nitrogen.

Cover crops (rye, clover, buckwheat) protect bare soil from erosion between crops; a green manure is a cover crop grown specifically to be tilled into the soil to add organic matter (and, for legumes such as clover or vetch, nitrogen). Crop rotation moves plant families to new beds each year: it breaks pest and disease cycles and balances nutrient use, because growing the same crop in the same spot repeatedly draws down the same nutrients and builds up its pests. The classic sequence plants a heavy nitrogen feeder such as corn after a legume that left fixed nitrogen behind. Monoculture (one crop over a large area) is efficient but highly vulnerable to pests and disease. Companion planting pairs plants that help each other: the "Three Sisters" of corn (a stalk for beans to climb), beans (nitrogen fixation) and squash (big leaves shade out weeds and hold soil moisture); marigolds, which suppress root-knot nematodes and are said to deter some insects; nasturtiums as a trap crop that draws aphids and squash pests away; and herbs such as mint that repel some pests (mint itself spreads so aggressively by rhizomes that gardeners grow it in containers).

Fertilizers

A fertilizer grade (analysis) lists three numbers, always in the order N-P-K: the percent by weight of total nitrogen (N), available phosphate (expressed as P₂O₅) and soluble potash (expressed as K₂O). A complete fertilizer contains all three. Nitrogen drives leafy growth and green color; phosphorus supports roots, flowering and energy transfer (ATP); potassium supports stomatal control, disease resistance and strong stems.

A balanced or all-purpose fertilizer has equal numbers (10-10-10, 20-20-20); a starter or "bloom" fertilizer is high in phosphorus (10-20-10); single-nutrient fertilizers include urea (46-0-0), ammonium nitrate (34-0-0), ammonium sulfate (21-0-0), triple superphosphate (0-46-0) and muriate of potash (0-0-60). Plants take up phosphorus as orthophosphate ions (H₂PO₄⁻ and HPO₄²⁻); polyphosphate fertilizers must first break down to orthophosphate in the soil. Inorganic (synthetic) fertilizers are concentrated, fast-acting and have an exact analysis, but they add no organic matter, leach easily and can "burn" plants. Organic fertilizers (manure, compost, bone meal, blood meal, fish emulsion) release nutrients slowly because soil microbes must break them down first, so they are mixed into moist soil ahead of planting; they improve soil structure but have low and variable nutrient content. Poultry manure is richer in nitrogen than cow manure. Slow-release (coated) fertilizers meter nutrients out over weeks to months.

Ways to apply: broadcasting (spreading evenly over the whole surface), banding (in a strip beside the seed row at planting), side-dressing (along a row or in a ring around a plant during the season), top-dressing (on the surface of turf or an established bed), foliar feeding (spraying dilute nutrients on leaves) and fertigation (through irrigation water). Over-fertilizing causes salt buildup that pulls water out of roots (fertilizer burn, soil salinization), pollutes water through runoff and, with too much nitrogen, gives lush leaves and few flowers or fruits, which is why flowering plants are not switched to a high-nitrogen fertilizer once they bloom.

Climate, site and timing

The USDA Plant Hardiness Zone Map divides North America by the average annual extreme minimum winter temperature (the coldest night of an average year). Each zone spans 10 °F and is split into "a" and "b" halves of 5 °F; zone 7, for example, has average minimums of 0 to 10 °F, and zone 5 has −20 to −10 °F. The contiguous United States runs from about zone 3 (northern Minnesota, North Dakota) to zone 10 or 11 (southern Florida). The 2023 update shifted about half the country into the next warmer half-zone, consistent with warming winters. Hardiness zones say nothing about summer heat; the American Horticultural Society's Heat Zone Map counts days above 86 °F for that.

A microclimate is a local climate that differs from the area around it: a bed against a sunny, south-facing wall is warmer, and a low-lying open spot is a frost pocket because cold, dense air drains downhill and pools there on clear, still nights. Many temperate fruit trees and bulbs need a minimum number of chilling hours (hours at cool temperatures, roughly 32 to 45 °F) to break dormancy and bloom evenly; this is why spring-flowering bulbs such as tulips, daffodils and crocuses are planted in fall.

Fruit crops have climate limits. Citrus is subtropical and frost-tender, grown outdoors in the U.S. only in about zones 9 to 11 (Florida, Texas, California, Arizona) and elsewhere in containers moved indoors; mangoes, bananas and papayas need frost-free tropical conditions. Figs grow outdoors in about zones 7 to 10 (hardier cultivars into zone 6 with protection). Apples (roughly zones 3 to 8), pears and sweet cherries need winter chilling, so they do poorly in the warmest zones; peaches grow in about zones 5 to 9. Strawberries are grown almost everywhere except the hottest zones, where they are treated as winter annuals. European pears (Bartlett, d'Anjou, Bosc) are pear-shaped with soft, buttery flesh and are picked mature but hard, then ripened off the tree; Asian pears (nashi) are round, crisp and juicy like an apple and ripen on the tree.

Hedges use dense shrubs that tolerate repeated shearing: privet, boxwood, yew, holly, arborvitae, hornbeam and beech, plus barberry or roses where a spiny barrier is wanted. Shear hedges slightly narrower at the top than at the base so the lower branches get light and stay leafy.

Cherries: tart (sour) cherries are self-fruitful, but most sweet cherries are self-unfruitful and need a second, compatible cultivar nearby for pollination (a few, such as 'Stella' and 'Lapins', are self-fertile). Both bloom early, so spring frosts can kill the flowers; birds take much of the crop unless trees are netted; and rain on ripening sweet cherries makes them crack.

Intensive beds. Square-foot gardening divides a bed into 1-foot squares and plants each square at a fixed density instead of in rows: typically 1 large plant (tomato, pepper), 4 medium plants (lettuce, marigold), 9 (beets, spinach, bush beans) or 16 small plants (carrots, radishes, onions) per square. So 16 carrots per square foot means one carrot every 3 inches each way, and a 4 × 4 ft bed of carrots holds 16 × 16 = 256 plants. Proper spacing gives each plant light, water and nutrients and lets air move, reducing disease; crowding gives small, spindly plants.

Gardeners in deer country choose plants deer avoid: aromatic or strongly scented foliage (lavender, sage, rosemary, mint, Russian sage), fuzzy or hairy leaves (lamb's ear), toxic plants (daffodils, foxglove), and tough, spiny or leathery foliage (barberry, boxwood, many ferns and ornamental grasses). Deer favorites include hostas, tulips, daylilies and arborvitae.

Cool-season vegetables grow best in spring and fall and tolerate light frost: lettuce, spinach, peas, radishes, broccoli, cabbage, cauliflower, kale, carrots, beets and onions. Many bolt (flower and turn bitter) in summer heat. Warm-season vegetables are frost-tender and need warm soil: tomatoes, peppers, eggplant, cucumbers, squash, melons, beans, sweet corn and okra. They are planted after the last frost date (cucumbers about two to three weeks after it, once the soil has warmed). Spinach is a classic cool-season, frost-hardy, long-day crop: it is sown in early spring or fall and bolts quickly as days lengthen and heat rises. Cauliflower is a cool-season crop too, but in India and other tropical regions early, heat-tolerant cultivars are grown through the warm, rainy monsoon season.

Seed-starting rules of thumb: plant a seed about two to three times as deep as its diameter, so tiny carrot seeds go only about 1/4 inch deep and lettuce seed is barely covered (about 1/8 inch or pressed onto the surface, since many lettuce cultivars need light to germinate); marigolds go about 1/8 to 1/4 inch, and beans about 1 inch. Most vegetable seeds germinate fastest in warm soil (beans near 80 °F; most warm-season seeds in the 70s to mid-80s °F), and seedlings indoors need strong light for many hours a day or they stretch (etiolate). Start tomatoes and marigolds indoors about 6 to 8 weeks before the last frost. The first leaves most seedlings show are their cotyledons (seed leaves), which look different from the plant's later leaves; seedlings are transplanted or thinned once they have one or two sets of true leaves. Hardening off is gradually exposing indoor-grown seedlings to outdoor sun, wind and cool nights over about one to two weeks before transplanting, so they do not suffer transplant shock. A seed drill places seeds at an even depth and spacing in rows, the opposite of broadcasting seed by scattering it. When transplanting a container plant whose roots circle the pot (root-bound), tease the roots apart or score or slice the root ball vertically in a few places so new roots grow outward into the soil instead of continuing to circle.

Water, protected growing and soilless culture

Drip irrigation delivers water slowly to the root zone through emitters and conserves the most water; overhead sprinklers lose water to evaporation and wind and wet the leaves, which spreads foliar disease; flood and furrow irrigation are the least efficient. Water in the morning so roots take up water before the heat of the day and leaves dry quickly. Deep, infrequent watering grows deeper roots than frequent sprinkles. Too much water is as harmful as too little: waterlogged soil has no oxygen, so roots die and root rot sets in, which is why pots need drainage holes. Uneven watering (dry spells then a soaking) makes tomatoes crack and contributes to blossom-end rot (a calcium-supply problem; see Nutrient deficiencies).

Xeriscaping is landscaping designed to reduce or eliminate irrigation: planning and zoning plants by water need, improving soil, limiting thirsty turf, choosing drought-tolerant and native plants (lavender, succulents, ornamental grasses), efficient irrigation such as drip, and mulching. The three basics of lawn care are mowing (never removing more than about one-third of the blade at a time), watering (deep and infrequent) and fertilizing. Mowing in the same direction every time pushes grass blades to lean and compacts wheel tracks, so alternate the pattern. Delaying spring mowing ("No Mow May") or mowing higher and less often lets dandelions, clover and violets flower for early-season bees.

A greenhouse regulates temperature (and light and humidity) so crops can be grown out of season; cold frames, hotbeds, high tunnels (hoop houses) and floating row covers are cheaper season extenders. Most houseplants and many greenhouse crops grow well at roughly 65 to 75 °F by day with nights about 10 °F cooler; tropical foliage plants are damaged by temperatures much below 50 °F. Hydroponics grows plants without soil, with roots in a mineral nutrient solution (sometimes supported by an inert medium such as rockwool, perlite or clay pebbles). Common systems:

Hydroponics uses far less water than field growing, gives fast growth and high yields in a small space, avoids soil pests and weeds and runs year-round. Its drawbacks are high startup cost, dependence on pumps and power, the need to monitor solution pH (about 5.5 to 6.5) and nutrient strength (electrical conductivity), and the risk that a root disease (such as Pythium) spreads quickly through shared water. Leafy greens, lettuce and herbs are the classic hydroponic crops, followed by tomatoes, cucumbers, peppers and strawberries. Hydroculture is the broader term for growing plants in water or an inert medium instead of soil; hydroponics is one form of it.

Harvest, storage and plant protection

• Onions are left until their tops fall over and dry, then cured (dried in a warm, airy place for a few weeks) and stored cool and dry.
• Bulb foliage must be left to die back naturally: the leaves keep photosynthesizing and refill the bulb for next year. Tender bulbs and tubers that are dug for winter (dahlias, gladiolus) are stored cool, around 40 to 50 °F, and dry.
• Cut flowers last longest when harvested in the cool of morning or evening, cut with clean, sharp tools, re-cut at an angle under water, placed promptly in clean water (often acidified and with sugar and a biocide in commercial floral preservatives) and kept cool and away from ripening fruit, whose ethylene speeds wilting.
• Apples keep for months in controlled-atmosphere storage: low temperature, low oxygen and raised CO₂ slow respiration and ripening; 1-MCP blocks ethylene receptors.
• Blanching in the garden means excluding light from part of a growing plant (tying leaves over a cauliflower head, hilling soil around leeks or celery) so it stays pale, tender and mild. The cost is extra labor, a higher risk of rot under the cover and fewer light-dependent nutrients.
• Integrated pest management (IPM) combines monitoring and action thresholds with cultural controls (resistant cultivars, rotation, sanitation, spacing for airflow), mechanical controls (hand-picking, row covers, traps), biological controls and, only as needed, targeted pesticides. Biological controls include lady beetles and lacewing larvae against aphids, parasitic wasps (Trichogramma attacks moth eggs; Encarsia attacks whiteflies), predatory mites against spider mites, beneficial nematodes against soil grubs, Bacillus thuringiensis (Bt) sprays against caterpillars, and insect viruses such as nuclear polyhedrosis virus. Biological control is targeted, avoids chemical residues and is slow for pests to evolve resistance to, and an established natural enemy can keep working for years; but it acts slowly, works best on low or moderate pest levels, needs careful timing and conditions, can fail if the agent does not establish, and an introduced agent can attack non-target species (as the cane toad and some introduced weevils did). The soil fumigant methyl bromide was phased out under the Montreal Protocol because it depletes stratospheric ozone. IPM's environmental benefits: less pesticide in soil and water, less bioaccumulation and biomagnification up food chains, less harm to pollinators and natural enemies, slower evolution of pesticide resistance, and fewer spray passes (less fuel, CO₂ and soil compaction). Mixed cropping (intercropping) and mulching also reduce pests by hiding hosts, harboring predators and blocking soil-borne spores from splashing onto leaves.

Common garden pests: aphids (small, soft, sap-sucking insects; they excrete sticky honeydew that grows sooty mold, are tended by ants and transmit plant viruses), whiteflies, spider mites (stippled leaves and fine webbing), thrips, scale insects and mealybugs, flea beetles (tiny jumping beetles that chew shot holes in seedlings of tomatoes, peppers, eggplant, potatoes and cabbage-family crops), cucumber beetles (which also spread bacterial wilt), squash vine borers (moth larvae that tunnel into the stems of squash, pumpkins and other gourds), the Colorado potato beetle, tomato hornworms, Japanese beetles, slugs and snails, and vertebrates such as deer, rabbits and voles (which eat roots, bulbs and bark below ground or under snow).

Plant breeding

Breeders improve crops by selection (keeping the best plants each generation), hybridization (crossing parents to combine traits, then selecting), mutation breeding, marker-assisted selection and genetic engineering (see Genetically modified organisms). Recurrent selection repeatedly selects superior individuals and intercrosses them; progress per cycle (response to selection) rises with more additive genetic variance and stronger selection. A cultivar name is written in single quotes after the species name, as in Malus domestica 'Honeycrisp'. Heritability measures how much of the variation in a trait is genetic: broad-sense heritability H² = V_G / V_P (all genetic variance over total phenotypic variance) and narrow-sense heritability h² = V_A / V_P (only the additive variance, which is what parents reliably pass to offspring). Breeders use the breeder's equation, R = h² × S, where S is the selection differential (how far the selected parents' mean is above the population mean) and R the response in the next generation; a trait with h² = 0.5 and S = 10 cm should gain about 5 cm. Dominance and epistasis variance are not passed on predictably through sexual crosses, but they can be captured in clones and F₁ hybrids. Breeding goals include yield, pest and disease resistance, drought tolerance, quality, shelf life and plant form (dwarfing).

Practices and materials at a glance

Many horticulture questions come down to one practice or material: what it is, why and when a gardener uses it, and what goes wrong. The table below gathers those facts in one place, grouped by category so you can scan a whole topic (soil pH, compost, pruning, storage, pest control, lawns) at once. Values are typical U.S. extension figures; real products and regions vary, so treat numbers as "about". Use the Category column to filter, and read the Cautions column for the common "true or false" traps.

ReferenceGardening and horticulture practices· 134 rows

Fertilizer grades are N-P₂O₅-K₂O percentages. "Raises pH" = makes soil less acidic. Temperatures in °F unless marked. IPM = integrated pest management.

134 rows

Practice or material	Category	What it is	Why and when	Cautions
Lime: ground limestone (calcitic), dolomitic, hydrated or quicklime	Amendment; raises pH	Calcium carbonate; calcium magnesium carbonate; calcium hydroxide or oxide	Corrects acid soil and adds Ca (dolomitic also Mg); rate from a soil test's lime requirement; fall application reacts by spring; hydrated lime acts fastest	Limestone is slow (months; finer grind faster); hydrated lime is caustic and easy to overshoot; over-liming locks up Fe, Mn, Zn, P; dolomitic adds unneeded Mg on high-Mg soils
Wood ash	Amendment; raises pH	Ash of burned untreated wood; mostly Ca and K carbonates, some P	Weaker liming agent than limestone; supplies K	Not on alkaline soil, blueberries or potato ground (higher pH favors scab); no ash from coal, charcoal briquettes or treated wood
Eggshells	Amendment; raises pH	Calcium carbonate	Slow Ca source; often added at tomato planting against blossom-end rot	Break down slowly; blossom-end rot is mostly uneven watering, not low soil Ca
Elemental sulfur	Amendment; lowers pH	Yellow S; soil bacteria oxidize it to sulfuric acid	Acidifies for blueberries (pH 4.5 to 5.5), azaleas, rhododendrons; apply months ahead	Slow, needs warm moist soil; clay and high-lime soils need much more; overdose hard to reverse
Aluminum sulfate; iron sulfate	Amendment; lowers pH	Salts that acidify quickly	Fast acidification; Al turns bigleaf hydrangea blue; iron sulfate also supplies Fe and greens chlorotic plants	Repeated Al builds toxic Al³⁺; iron sulfate stains concrete rust-orange
Ammonium sulfate (21-0-0)	Fertilizer; lowers pH	Synthetic N with S	N for acid-loving plants; most acidifying common N source	Can burn; long use acidifies most soils (calcareous soils resist)
Gypsum	Amendment; little pH change	Calcium sulfate	Adds Ca and S without liming; reclaims sodic (sodium) soils by displacing Na	Does not loosen ordinary non-sodic clay; does not raise pH
Sphagnum peat moss; coir	Medium	Partly decayed Sphagnum (pH about 3.5 to 4.5); coconut husk fiber (near neutral)	Water holding and light weight; base of soilless mixes; coir is the renewable substitute	Peat is nonrenewable (bogs store carbon) and repels water when dry; coir can be salty, so buy it rinsed
Perlite; pumice	Medium	Heated, popped volcanic glass; porous volcanic rock; both neutral and inert	Aeration and drainage in potting, rooting and cactus mixes; pumice is heavier and is less likely than perlite to float to the top	Hold little water or nutrients; perlite dust (wet it first)
Vermiculite	Medium	Heated, expanded mica-like mineral	Holds water and nutrients (high CEC); seed starting; covers fine seeds	Compresses over time; old Libby, Montana ore was asbestos-contaminated
Sand	Amendment	Coarse mineral particles	Drainage in raised-bed or cactus mixes	A little sand in clay can set like concrete; needs about half the volume to help
Biochar	Amendment	Charcoal made by pyrolysis (heating biomass with little oxygen)	Long-lasting carbon; raises CEC and water holding; carbon storage	Usually alkaline; fresh char can tie up nutrients, so charge it in compost first
Compost; leaf mold	Amendment	Decomposed organic matter (dark, crumbly, earthy smell); leaves decayed mainly by fungi over 1 to 2 years	Soil conditioner for any soil, 1 to 3 in worked in yearly; leaf mold is an excellent mulch	Low, variable nutrients; immature compost ties up N and can harm seedlings
Sawdust, fresh wood chips (mixed into soil)	Amendment	Very high C:N wood (several hundred to 1)	Adds organic matter slowly	Microbes borrow soil N while decaying it (N tie-up, yellow plants); add N; less of a problem as a surface mulch
Coffee grounds (used)	Amendment; compost green	About 2% N; near-neutral pH once brewed	A "green" for compost; thin mulch layer	Not strongly acidic; thick layers crust and shed water
Pine needles (pine straw)	Mulch	Fallen conifer needles	Loose, long-lasting mulch that stays in place on slopes; popular for azaleas	Barely change soil pH; flammable when dry
Epsom salt	Fertilizer; Mg	Magnesium sulfate	Corrects a confirmed Mg deficiency (yellowing between veins of old leaves); foliar spray	No benefit if Mg is adequate; excess competes with Ca and K
Chelated iron	Fertilizer; micronutrient	Fe held soluble by an organic chelate (EDTA, DTPA, EDDHA)	Treats iron chlorosis of young leaves in alkaline soil; EDDHA works at the highest pH	Treats the symptom; the cause is usually high pH, so test pH first
Blood meal	Fertilizer; organic	Dried blood, about 12-0-0	Fast organic N for leafy growth	Can burn like synthetic N; attracts dogs and animals
Bone meal	Fertilizer; organic	Steamed ground bones, about 3-15-0 plus Ca	Traditional P source at planting for bulbs and roots	P barely available above about pH 7; attracts digging animals
Fish emulsion; fish meal	Fertilizer; organic	Liquid fish by-product, about 5-1-1	Quick liquid N for transplants and containers	Strong odor
Other organic fertilizers	Fertilizer; organic	Cottonseed meal (about 6-2-1, mildly acidifying); kelp meal (mostly K and trace elements); rock phosphate (slow P); greensand (glauconite, slow K)	Cottonseed meal for acid-loving shrubs; kelp for micronutrients and foliar sprays; rock phosphate and greensand as long-term reserves	Rock phosphate works only in acid soil; all act slowly; kelp contains salt
Organic vs. synthetic fertilizer	Fertilizer	Organic: from living things, low analysis; synthetic: manufactured salts, high analysis	Organic: slow, feeds soil life, improves structure; synthetic: fast, exact, cheap per pound of N	Organic N must be mineralized by microbes (slow in cold soil); plants absorb the same ions either way; synthetic salts can burn and leach
Complete, balanced and starter fertilizers	Fertilizer; synthetic	Complete has N, P and K; balanced has equal numbers (10-10-10); starter is high-P and soluble (10-20-10)	General feeding when no test is done; starter for root growth of transplants	Unneeded P builds up and pollutes water; salts near roots burn
Urea (46-0-0)	Fertilizer; synthetic	Highest-N solid fertilizer; converted to ammonium by urease	Cheap N for lawns and crops	Left on the surface it loses N as ammonia gas; water it in
Ammonium nitrate (34-0-0)	Fertilizer; synthetic	Half nitrate (instant), half ammonium	Fast N	Oxidizer and explosive hazard; sale restricted
Calcium nitrate (15.5-0-0)	Fertilizer; synthetic	Nitrate N plus soluble Ca	Tomatoes, peppers and hydroponics against blossom-end rot; does not acidify	Absorbs moisture from air (cakes)
Superphosphate (0-20-0), triple superphosphate (0-46-0); muriate of potash (0-0-60), sulfate of potash (0-0-50)	Fertilizer; synthetic	Acid-treated rock phosphate (also MAP 11-52-0, DAP 18-46-0); potassium chloride; potassium sulfate	P for roots and flowering; K for fruit, stems and disease resistance	P moves little, so place it in the root zone; KCl has a high salt index and chloride harms sensitive crops (potatoes, tobacco, strawberries)
Slow-release vs. water-soluble fertilizer	Fertilizer	Polymer-coated prills (Osmocote-type), sulfur-coated urea or urea-formaldehyde; dissolved fertilizer such as 20-20-20, also used for foliar feeding	Slow-release feeds for months with less burn and leaching; soluble gives quick feeding of containers and transplants	Slow-release releases faster in heat and costs more; soluble is short-lived and burns leaves if strong or in hot sun
Late-season fertilizing of woody plants	Fertilizer timing	High-N feeding in late summer	Avoid it: feed in early spring	Pushes soft growth that winter kills; excess N favors leaves over flowers
C:N ratio in composting	Compost	Carbon-to-nitrogen balance of the pile	Aim for about 25 to 30:1, often about 2 to 3 parts brown to 1 part green by volume	Too much C: slow, cold pile; too much N: ammonia smell
Browns and greens	Compost	Browns: dry, carbon-rich (dead leaves about 60:1, straw about 80:1, sawdust, shredded paper, cardboard); greens: moist, N-rich (grass clippings about 20:1, fruit and vegetable scraps about 15:1, coffee grounds, fresh herbivore manure)	Browns give energy and structure; greens supply N and heat the pile	No glossy paper or treated wood; thick mats of clippings go slimy and anaerobic, so layer or mix
Hot vs. cold composting	Compost	Hot: large (about 3 × 3 × 3 ft or more), moist, turned pile; cold: unturned heap	Hot reaches 130 to 160 °F, kills most weed seeds and pathogens, done in weeks to months (mesophilic → thermophilic → cooling and curing); cold is low effort, done in 6 to 24 months	Above about 160 °F kills beneficial microbes; keep moist like a wrung-out sponge and turn when it cools; cold piles do not kill seeds or pathogens
What not to compost	Compost	Meat, fish, bones, dairy, fats and oils; dog, cat or pig feces; diseased plants; weeds with seeds or runners; black walnut debris; treated wood; coal ash	Avoids odors, rats, raccoons, flies and spreading pathogens or weeds	Diseased material only in a pile that truly gets hot; walnut (juglone) breaks down after long composting
Vermicomposting	Compost	Bins of red wigglers (Eisenia fetida), not nightworms	Turns kitchen scraps into castings; works indoors	Avoid too much citrus, onion and meat; keep moist and below about 80 °F
Animal manures	Manure	Fresh N roughly: cow about 0.5%, horse about 0.7%, sheep about 1%, chicken about 1 to 1.5% (more when dried), rabbit about 2%	Organic matter plus N; poultry richest ("hot"), cow mildest	Fresh "hot" manure burns plants; horse and cow manure can carry weed seeds and persistent herbicides (aminopyralid, clopyralid) that cripple tomatoes and beans
Manure safety	Manure	Rules for manure on food crops	Compost or age it first. U.S. organic rules: raw manure at least 120 days before harvest if the edible part touches soil, 90 days otherwise; composted manure must hold 131 to 170 °F for 3 days (in-vessel or static pile) or 15 days with 5 turnings (windrow)	E. coli O157:H7, Salmonella; never dog, cat or pig manure on food crops (roundworms, Toxoplasma); still wash produce
Straw; grass clippings	Mulch	Dry grain stems; dried lawn clippings in thin layers	Straw for vegetable rows and paths, keeps strawberries and squash clean; clippings are a free N-rich mulch	Use straw, not hay (full of seeds); straw cools soil, so wait for warm soil under warm crops; no clippings from herbicide-treated lawns
Shredded bark, wood chips	Mulch	Tree bark or chipped wood, 2 to 4 in deep	Perennial beds and trees; suppress weeds, hold water, add organic matter	Keep a few inches off trunks (no "mulch volcanoes"); slight N tie-up only at the surface
Rubber mulch; gravel and stone	Mulch; inorganic	Shredded recycled tires; rock layer	Rubber lasts on playgrounds; rock suits xeriscapes and succulents	Neither adds organic matter; rubber can leach zinc, heats up and burns; rock reflects heat
Black and reflective (silver) plastic mulch	Mulch; inorganic	Polyethylene or metallized film over the bed	Black warms soil for melons, tomatoes and peppers, stops weeds, keeps fruit clean; silver repels aphids and thrips that spread viruses	Need drip tubing underneath; disposal waste; silver keeps soil cooler than black
Clear plastic; soil solarization	Mulch; weed and disease control	Clear plastic sealed over moist, bare soil in the hottest weeks of summer for 4 to 6 weeks	Heats the top inches enough to kill many weed seeds, nematodes and soilborne pathogens	Clear plastic as a growing mulch lets weeds grow underneath
Landscape fabric	Mulch; inorganic	Woven or spun weed-barrier cloth under rock or bark	Blocks weeds while passing water and air	Weeds root into organic mulch on top; roots grow into it; poor for beds you replant
Living mulch	Mulch; cropping	Low cover crop (clover) grown between crop rows	Covers soil, adds N, feeds beneficial insects	Competes for water and nutrients if not mowed
Germination conditions	Seeds	Needs water, oxygen and suitable temperature; some seeds need light	Most warm-season seeds germinate best near 75 to 85 °F; cool-season crops germinate in cooler soil	Light-requiring seeds (lettuce, petunia, impatiens, begonia) go on the surface; soggy media starve seeds of oxygen
Scarification; stratification	Seeds	Nicking, sanding, hot water or acid on a hard seed coat; cold, moist storage (about 34 to 41 °F) for weeks	Scarify morning glory, sweet pea, lupine, okra, redbud; stratify many temperate trees, shrubs and wildflowers (milkweed, apples, many natives) to break embryo dormancy	Do not damage the embryo; stratification must be moist cold, not dry; fall sowing outdoors does it naturally
Seed-starting medium; damping-off	Seeds	Sterile, fine, soilless mix (peat or coir, vermiculite, perlite); damping-off is seedling rot at the soil line (Pythium, Rhizoctonia, Fusarium)	Even moisture and air, no pathogens or weed seeds; prevent damping-off with clean pots, bottom watering, airflow and spacing	Garden soil compacts and carries the fungi; overwatering, cool wet media and low light favor damping-off
Seed storage and viability	Seeds	Keep seeds cool, dark and dry (sealed jar in a refrigerator)	Rule of thumb: storage °F + % relative humidity under 100; a rag-doll (paper towel) test checks germination %	Onion and parsnip seed are short-lived (about 1 year); leek about 2 years
Thinning	Planting	Removing extra seedlings to the final spacing	When seedlings have 1 to 2 true leaves; gives each plant light, water, air	Snip with scissors rather than pull, so neighbors' roots are not disturbed
Transplanting	Planting	Moving seedlings to the garden	Cloudy day or evening; water in; most plants set at the same depth	Tomatoes can go deeper (stems root); taprooted and root crops (carrots, beets) and squash family resent transplanting, so direct-seed them
Hardening off	Planting	Gradually exposing indoor seedlings to sun, wind and cooler nights	Over about 7 to 14 days before transplanting; reduce water a little	Skipping it causes sunscald, wilting and transplant shock
Succession planting	Cropping system	Sowing small batches every 2 to 3 weeks, or following one crop with another	Steady harvest of lettuce, radishes, beans, sweet corn; e.g. fall carrots after spring peas	Late sowings must mature before frost
Intercropping	Cropping system	Two or more crops in the same space at once	Uses space and time; fast radishes between slow carrots; Three Sisters (corn as pole, beans fix N, squash shades weeds)	Crops compete if spacing or timing is wrong
Companion planting; trap crops	Cropping system	Pairing plants for claimed benefits; a more attractive plant that draws pests away	French marigolds grown densely suppress root-knot nematodes; flowers draw beneficial insects; nasturtium or blue hubbard squash as traps for squash bugs and cucumber beetles	Many pairings are folklore; trap crops must be destroyed or sprayed or they breed pests; some plants are allelopathic (black walnut)
Crop rotation	Cropping system	Moving plant families to new beds each year, typically a 3- to 4-year cycle	Breaks pest and disease cycles; balances nutrients (legume → heavy feeder such as corn → light feeder such as root crops)	Rotate by family: tomato, potato, pepper and eggplant count as one (Solanaceae), so soilborne wilts persist for years
Non-legume cover crops	Cover crop	Cereal (winter) rye; oats; buckwheat; tillage radish	Rye: hardy, holds soil, scavenges N, big biomass; oats winter-kill in cold zones; buckwheat: fast summer smother crop that flowers in weeks, feeds pollinators, mobilizes P; radish taproots break compaction	Rye is allelopathic to small seeds and tough to kill when tall (not the same as ryegrass); mow buckwheat before seed set
Legume cover crops (hairy vetch, crimson clover, field peas)	Cover crop	Nitrogen-fixing cover crops	Add N for the next crop; tilled or cut as green manure in spring	Need the right Rhizobium inoculant; vetch can reseed as a weed
Rhizobium inoculant	Planting	Peat-based bacteria coated on legume seed	Ensures nodules and N fixation where that legume has not grown recently	Strains are crop-specific (pea and bean groups differ); live product, keep cool
Tillage vs. no-till	Soil care	Plowing, rototilling or double digging; or planting into undisturbed soil and residue	Tillage prepares a seedbed, aerates, buries residue and weeds; no-till cuts erosion, builds organic matter and soil life, saves water	Tillage destroys structure, speeds organic-matter loss and erosion, forms a plow pan (never work wet soil); no-till relies more on mulch, cover crops or herbicides and warms slowly
Raised beds	Planting	Soil built up 6 to 12 in or more, often framed	Better drainage, earlier warming, no walking on soil; keep 3 to 4 ft wide to reach the middle	Dry out faster; frames cost; avoid old pressure-treated or creosote wood
Hilling	Planting	Mounding soil around stems	Potatoes: covers tubers so they do not turn green (solanine) and adds room for tubers; also leeks	Hilling too close damages roots
Drip irrigation; soaker hoses	Water	Slow water to the root zone through emitters or porous hose	Most efficient (often about 90%); leaves stay dry, so less foliar disease; good under plastic mulch	Clogging; needs filters and pressure regulators
Sprinkler, furrow and flood irrigation	Water	Overhead spray; water run down channels or across fields	Sprinklers for lawns, large areas and frost protection; furrow and flood where water is cheap (rice paddies)	Sprinklers lose water to wind and evaporation and wet leaves (disease); furrow and flood are least efficient and build salts
How much to water	Water	About 1 in per week (rain plus irrigation) for most gardens and lawns	Deep, infrequent watering builds deep roots; water in the morning; check soil 2 in down	Containers dry daily in summer; overwatering suffocates roots
Containers	Planting	Plants in pots	Need drainage holes and a light soilless mix; repot into a pot 1 to 2 in wider when rootbound	A gravel layer at the bottom does not help drainage; it raises the perched water table
Heading vs. thinning cuts	Pruning	Heading: back to a bud; thinning: whole branch to its origin	Heading thickens growth below the cut; thinning opens the canopy with little regrowth	Heading at random spots (topping, shearing) makes dense weak sprouts
Pruning timing	Pruning	Matching cuts to where flowers form and to disease risk	Spring bloomers on old wood (forsythia, lilac, azalea): right after flowering; summer bloomers on new wood (butterfly bush, panicle hydrangea, crape myrtle): late winter; fruit trees: dormant late winter; oaks: dormant season (winter)	Winter pruning of old-wood bloomers removes this spring's flowers; pruning oaks in spring and early summer lets sap beetles spread oak wilt
Hydrangea pruning	Pruning	Depends on species	Bigleaf and oakleaf bloom on old wood (prune after flowering); panicle and smooth (Annabelle) bloom on new wood (late winter)	Wrong timing means no flowers; reblooming bigleaf cultivars bloom on both
Roses	Pruning	Cutting canes to outward buds	Hybrid teas in early spring as buds swell; once-blooming climbers and ramblers right after flowering	Remove suckers from below the graft union at their origin; no need to seal cuts
Conifers and evergreens	Pruning	Light cuts into green growth	Pines: snap new "candles" by half in late spring; shear hedges early summer	Most conifers (pine, spruce, arborvitae, juniper) will not resprout from bare old wood; yew can
Brambles (raspberry, blackberry)	Pruning	Canes are biennial: first-year primocanes, second-year floricanes	Summer-bearing: remove floricanes after harvest; fall-bearing: mow all canes in late winter for one fall crop	Leaving dead floricanes harbors disease
Grapes	Pruning	Cane or spur pruning while dormant	Fruit forms on current-season shoots from 1-year-old wood; remove about 80 to 90% of last year's growth	Underpruned vines overcrop and ripen poorly; heavy "bleeding" sap in spring is harmless
Fruit-tree training	Training	Shaping young trees	Central leader (apple, pear); modified leader; open center or vase (peach, plum) for light	Wide crotch angles are strong; narrow V crotches split
Espalier, cordon, topiary, bonsai, pleaching, coppicing, pollarding	Training	Flat-trained on a wall; single-stem fruit tree; sheared shapes; miniature potted trees; interwoven branches; cut to ground; cut to head height	Space-saving, decorative or wood-producing forms	Need regular, timed pruning; not all species tolerate coppicing
Tomato support; suckering	Support	Stakes, cages or trellis; removing side shoots in leaf axils	Indeterminate vines keep growing and need tall support (sucker if staked); determinate bush types set fruit in one flush and need short cages	Do not sucker determinates (cuts yield); unsupported fruit rots on soil
Trellising	Support	Vertical netting, strings or frames	Pole beans, peas, cucumbers, small melons; saves space, cleaner fruit, better airflow	Heavy fruit needs slings; tendrils need thin supports
Tree staking and planting	Planting	Planting with root flare at soil level in a hole 2 to 3 times as wide as the root ball	Backfill with native soil; stake loosely only if needed and remove after about a year	Planting too deep and girdling roots kill trees; rigid staking weakens trunks
Deadheading; disbudding	Flowers	Removing spent flowers; removing side buds to leave one terminal bud	Deadheading gives more bloom and stops self-sowing; disbudding gives one large exhibition flower (chrysanthemum, peony, dahlia, carnation, camellia)	Leave seed heads for birds if wanted; disbudding means fewer flowers
Pinching	Flowers	Removing the shoot tip with fingers	Releases side buds for bushier plants (mums, basil, coleus, petunias)	Stop pinching garden mums by about early July or flower buds are lost
Stem cuttings	Propagation	Rooting shoot pieces, usually with auxin rooting hormone (IBA, NAA)	Softwood: late spring to early summer; semi-hardwood: mid to late summer (holly, azalea); hardwood: dormant season (willow, grape, forsythia, juniper)	Need humidity (mist, plastic tent) and bottom heat; no fertilizer until rooted
Leaf and root cuttings	Propagation	Leaf or leaf-petiole pieces; dormant root pieces	Leaf: African violet, Rex begonia, snake plant, jade; root: horseradish, blackberry, oriental poppy	Leaf cuttings of yellow-edged snake plant lose the edge (it is a chimera)
Layering	Propagation	Rooting a stem while still attached	Simple (bend a branch into soil), tip (black raspberry), serpentine (vines), mound or stool (apple rootstocks, currants), air (rubber plant, croton)	Slow (one season or more); few plants per parent
Grafting and budding	Propagation	Scion (desired cultivar) or a single bud joined to a rootstock, cambium to cambium	Whip-and-tongue and cleft in late winter to early spring with dormant scion wood; bark graft in spring when bark slips; T (shield) budding in summer when the stock's bark slips (roses, fruit trees); chip budding when it does not	Only between close relatives; keep scion wood dormant, cool and moist; remove rootstock shoots; a graft union buried in soil lets the scion root and lose dwarfing
Division	Propagation	Splitting clumps into rooted pieces	Spring bloomers in late summer or fall; summer and fall bloomers in spring; bearded iris after bloom in midsummer	Peony eyes no more than about 2 in deep or they will not bloom; iris rhizome tops at the surface
Spring bulb planting	Bulbs	Tulip, daffodil, crocus, hyacinth planted in fall	When soil cools (below about 60 °F), weeks before the ground freezes; depth about 2 to 3 times the bulb's height (tulips and daffodils 6 to 8 in), pointed end up	Leave foliage until it yellows (about 6 weeks) to refill the bulb; voles and squirrels eat tulips, not daffodils
Summer (tender) bulbs	Bulbs	Dahlia, gladiolus, canna, caladium, tuberous begonia	Plant after last frost in warm soil; in cold zones dig after frost blackens tops	Store dry and cool, about 40 to 50 °F (caladiums warmer, at or above about 60 °F); freezing or damp storage rots them
Forcing bulbs	Bulbs	Making bulbs bloom indoors out of season	Pot in fall, chill about 12 to 16 weeks at about 35 to 45 °F, then bring to warmth and light	Paperwhites and amaryllis need no chilling; keep bulbs away from ripening fruit (ethylene)
Photoperiod forcing	Flowers	Controlling day length to trigger bloom	Poinsettia and Christmas cactus are short-day plants: about 14 h of unbroken darkness nightly for 8 to 10 weeks from about October 1; mums forced with blackout cloth	A single light flash during the night resets it
Overwintering perennials	Winter	Winter mulch, hilling, bringing tender plants in	Mulch after the ground freezes to keep it frozen and prevent frost heaving; hill soil over rose crowns	Mulching early invites voles; potted plants' roots are far less hardy than in the ground
Winter protection of trees	Winter	Tree wraps, white trunk paint, guards, burlap screens	Prevents sunscald (southwest injury) on young thin-barked trees, rodent gnawing, and winter burn of evergreens	Remove wraps in spring (insects, girdling); water evergreens before freeze-up
Frost dates and growing degree days	Site and timing	Average last spring and first fall frost; GDD = (high + low)/2 minus a base, often 50 °F	Plant tender crops after the last frost; GDD and indicator-plant bloom (phenology, such as forsythia for crabgrass preventer) time planting and pest control	Averages, so frost is still possible after the date in about half of years
USDA hardiness zones; AHS heat zones	Site and timing	Average extreme winter minimum; average days above 86 °F	Choose perennials that survive winter cold and summer heat	Zones ignore snow cover, rainfall and microclimate
Frost protection	Frost and season	Covers, water and air movement on frost nights	Cover in the evening with cloth reaching the ground (traps soil heat); water soil the day before; orchards use wind machines or sprinklers (water releases heat of fusion as it freezes)	Plastic touching leaves conducts cold; sprinkling must continue until ice melts
Season-extension structures	Frost and season	Cold frame (bottomless box with clear lid); hotbed (same, heated by fresh manure or cables); row covers, cloches, low tunnels, Wall o' Water; high tunnel (unheated hoop house, crops in the ground)	Hardening off, early and late crops, overwintering greens; floating row cover also excludes insects; high tunnels extend the season by weeks to months	Vent on sunny days or plants cook; remove covers from squash and melons at bloom for pollination; salts and pests build up in tunnels
Greenhouse climate	Greenhouse	Heated, vented structure (glass, polycarbonate, double polyethylene)	Fan-and-pad evaporative cooling, shade cloth or whitewash, CO₂ enrichment (about 800 to 1,000 ppm), supplemental lighting	High humidity and still air favor Botrytis and powdery mildew
Greenhouse sanitation and monitoring	Greenhouse; IPM	Weed-free floors, clean benches, screened vents, sticky cards	Yellow cards catch whiteflies, aphids, fungus gnats, leafminers; blue cards catch thrips	Pests multiply year-round with no winter break
Hydroponic solution management	Hydroponics	Monitoring the nutrient solution; the passive Kratky method leaves roots in a non-circulating tank with a growing air gap	Keep pH about 5.5 to 6.5 and electrical conductivity (EC) in range; aerate; change or top up solution; Kratky needs no pump (lettuce, herbs)	Root rot (Pythium) spreads through shared water; warm water holds less oxygen; Kratky suits best short, fast crops
Aquaponics	Hydroponics	Fish tank plus hydroponic beds in one loop	Nitrifying bacteria turn fish ammonia into nitrate for plants	Must balance fish load, bacteria and plants; pesticides kill fish
Harvest indicators	Harvest	Signs of ripeness	Sweet corn: brown silks, milky kernel juice; watermelon: yellow ground spot, dried tendril; cantaloupe: full slip from vine; onions: tops fall over; potatoes: about 2 weeks after vines die; summer squash: small and glossy	Overmature beans and okra get tough; corn sugar turns to starch soon after picking
Field heat removal	Harvest	Cooling produce right after harvest	Hydrocooling (sweet corn), forced-air cooling (berries), vacuum cooling (lettuce), icing (broccoli)	Every hour warm shortens shelf life
Curing	Harvest and storage	Holding crops warm or dry to heal skins and finish them	Sweet potatoes 80 to 85 °F, high humidity, about 1 week; winter squash and pumpkins about 80 to 85 °F for 10 days (not acorn); onions and garlic dried warm and airy 2 to 3 weeks; potatoes 1 to 2 weeks cool and humid	Uncured crops rot or shrivel in storage
Storage conditions	Harvest and storage	Matching temperature and humidity to the crop	Cold and moist (about 32 °F, 90 to 95% RH): carrots, beets, cabbage, apples (a root cellar gives cool, humid storage); cool and dry: onions, garlic; potatoes about 40 to 45 °F, dark; sweet potatoes and winter squash about 50 to 60 °F	Potatoes too cold turn sweet, and in light turn green; store apples apart from vegetables
Chilling injury	Harvest and storage	Damage to tropical and subtropical produce above freezing (below about 50 °F)	Store tomatoes, basil, bananas, cucumbers, peppers, sweet potatoes cool, not cold	Pitting, water soaking, poor flavor; tomatoes lose flavor in the refrigerator
Ethylene management; controlled atmosphere	Harvest and storage	Ripening gas from apples, bananas, tomatoes; CA rooms with low O₂ and raised CO₂	Ripen climacteric fruit in a bag with a banana; 1-MCP blocks ethylene; CA slows respiration so apples keep for months	Keep ethylene producers away from carrots (bitter), lettuce (russet spotting), cut flowers and bulbs; too little O₂ causes fermentation
IPM framework and monitoring	IPM	Prevention, monitoring, thresholds, then the least-toxic effective control	Scout and identify with sticky cards, pheromone traps, degree-day models; act only at an action threshold; combine cultural, mechanical, biological, chemical tactics; time sprays to vulnerable life stages	Not "no pesticides"; misidentifying the pest wastes every later step; sex-pheromone traps usually catch only males and measure, not control
Cultural controls; resistant cultivars	IPM; cultural	Rotation, spacing, planting time, watering at soil level, healthy soil; seed-tag resistance codes	Tomato VFN(T): Verticillium wilt, Fusarium wilt, root-knot Nematodes, Tobacco mosaic virus; late squash avoids squash vine borer; airflow reduces fungi	Resistance covers listed strains only; needs planning ahead
Mechanical and physical controls	IPM; mechanical	Hand-picking, row covers, cutworm collars, water sprays, copper tape, beer traps, barriers	Exclude or remove pests without chemicals; strong water spray knocks off aphids and mites	Labor-intensive; row covers must be sealed and timed before pests arrive
Lady beetles; green lacewings	IPM; biological	Hippodamia convergens adults and larvae; Chrysoperla larvae ("aphid lions")	Aphids; lacewings also take mealybugs, mites, small caterpillars, insect eggs	Released lady beetles often fly off; their larvae look like tiny alligators, not pests; adult lacewings eat nectar and pollen
Parasitoid wasps	IPM; biological	Tiny wasps that lay eggs in or on hosts	Trichogramma: moth eggs; Encarsia formosa: greenhouse whitefly; Aphidius: aphids (leave tan "mummies"); Cotesia: hornworms (white cocoons on the back)	Broad-spectrum sprays kill them; leave parasitized hornworms
Other predators	IPM; biological	Predatory mites (Phytoseiulus persimilis), minute pirate bugs (Orius), mealybug destroyer (Cryptolaemus)	Spider mites; thrips; mealybugs	Work best in greenhouses with early release
Beneficial nematodes	IPM; biological	Steinernema and Heterorhabditis that carry insect-killing bacteria	White grubs, root weevils, fungus gnat larvae, soil-dwelling caterpillars	Apply to moist soil in the evening; UV and drying kill them
Bacillus thuringiensis (Bt)	IPM; biological	Bacterium whose Cry toxin is activated in alkaline insect guts	var. kurstaki: caterpillars; israelensis: mosquito, black fly and fungus gnat larvae; tenebrionis: Colorado potato beetle larvae	Must be eaten; breaks down in sunlight in days; also kills butterfly caterpillars
Milky spore and other microbials	IPM; biological	Paenibacillus popilliae; Beauveria bassiana (insect-killing fungus); Trichoderma and Bacillus subtilis (disease suppressors)	Japanese beetle grubs; whiteflies, thrips, aphids; root and leaf diseases	Milky spore is specific to Japanese beetle and takes years; fungi need humidity; most work as preventives
Insecticidal soap	IPM; chemical (low-risk)	Potassium salts of fatty acids	Soft-bodied pests (aphids, mites, whiteflies, mealybugs); contact only	No residual effect; must hit the pest; burns some plants in heat
Horticultural oil	IPM; chemical (low-risk)	Refined petroleum or plant oil; dormant or summer rates	Smothers scale, mites, eggs; dormant spray on fruit trees	Not above about 90 °F, on stressed plants, or near sulfur use; removes blue color from blue spruce
Neem; pyrethrins; spinosad	IPM; chemical (botanical, microbial)	Neem seed extract (azadirachtin); pyrethrum daisy flower extract; fermentation product of a soil bacterium	Repellent and growth regulator; fast knockdown; caterpillars, thrips, leafminers	Pyrethrins and wet spinosad harm bees and fish; pyrethroids are synthetic relatives
Copper, sulfur, Bordeaux mixture	IPM; chemical (fungicide)	Copper sulfate plus lime (Bordeaux, 1880s, grape downy mildew); elemental sulfur	Protectant fungicides and bactericides; must be on before infection	Copper builds up in soil; sulfur burns plants in heat or after oil sprays
Systemic insecticides	IPM; chemical	Absorbed and moved in the plant (neonicotinoids such as imidacloprid)	Long control of sap-feeders and borers	Reach pollen and nectar, harming bees; not on blooming plants
Pesticide label rules; resistance management	IPM; chemical	"The label is the law"; rotating modes of action	Signal words in rising toxicity: Caution, Warning, Danger; REI (re-entry interval); PHI (pre-harvest interval); rotation slows resistance in mites, whiteflies, weeds	Using on a crop not listed is illegal; repeating one product selects resistant survivors
Diatomaceous earth; kaolin clay	IPM; mechanical	Sharp fossil diatom shells; fine white clay film	Abrades and dries soft insects; clay coats fruit and repels pests (apple, pear)	DE useless when wet and harms beneficial insects; use food-grade, not pool-grade
Sanitation; roguing	IPM; sanitation	Removing diseased leaves, fallen fruit, debris and weeds; pulling infected or off-type plants	Removes overwintering pests and spores; disinfect tools with 70% alcohol or 10% bleach between plants; rogue virus, clubroot or wilt cases	Bag, do not compost; bleach corrodes tools; do not work among wet plants (spreads bacteria); smokers wash hands near tomatoes (tobacco mosaic)
Weed control (non-chemical)	Weeds	Mulch, hoeing, hand-pulling, stale seedbed, flame weeding, solarization	Remove weeds before they set seed ("one year's seeding, seven years' weeding")	Tilling brings buried weed seeds to the surface
Herbicide types	Weeds	Pre-emergent (stops seeds germinating); post-emergent; selective (2,4-D on broadleaves in lawns) vs. non-selective (glyphosate)	Crabgrass preventer goes on as soil reaches about 55 °F (forsythia bloom)	Pre-emergents also stop grass seed; drift damages grapes and tomatoes
Soil testing	Soil testing	Lab test from mixed subsamples, 0 to 6 in deep in gardens (shallower in lawns)	Every 3 to 4 years, often in fall; reports pH, lime need, P, K, Ca, Mg, organic matter, CEC	Use a clean plastic bucket (galvanized adds zinc); routine tests usually skip nitrate (it changes too fast)
Measuring pH; indicator plants	Soil testing	pH meter or indicator dyes in a soil-water slurry; plants whose color reports soil chemistry	Each unit is 10 times the acidity; most crops like 6.0 to 7.0; bigleaf hydrangea is blue in acid soil (Al available), pink in neutral to alkaline; red cabbage juice is a kitchen indicator	Cheap probe meters are unreliable; buffer pH, not soil pH, sets lime rate; white hydrangeas do not change
Texture tests	Soil testing	Ribbon (feel) test; jar (settling) test	In the jar, sand settles in a minute, silt in hours, clay in days	Organic matter floats and skews readings
Cool-season grasses	Lawn	Kentucky bluegrass, tall fescue, fine fescues, perennial ryegrass	Grow best about 60 to 75 °F; spring and fall growth; seed in late summer to early fall; most N in fall	Go dormant (brown) in summer drought
Warm-season grasses	Lawn	Bermudagrass, zoysia, St. Augustine, centipede, bahia, buffalograss	Grow best about 80 to 95 °F; plant and fertilize late spring to summer	Brown and dormant after frost; St. Augustine is planted as sod or plugs, not seed
Mowing	Lawn	Cutting height by species	Never remove more than one-third of the blade; roughly tall fescue 3 to 4 in, Kentucky bluegrass 2.5 to 3.5 in, bermudagrass and zoysia 1 to 2 in, St. Augustine 2.5 to 4 in; sharp blade; alternate direction; leave clippings	Scalping weakens turf and lets weeds in; dull blades shred tips
Core aeration; dethatching	Lawn	Pulling small soil plugs; vertical mowing or raking out thatch	Relieve compaction or thatch over about 1/2 in while grass grows strongly (fall or spring for cool-season, late spring or summer for warm-season)	Spike aerators can increase compaction; heavy dethatching tears turf; overfertilizing and overwatering build thatch
Overseeding and establishment	Lawn	Seed, sod, plugs or sprigs	Overseed thin cool-season lawns in early fall; sod gives instant cover; good seed-to-soil contact and constant light moisture	Pre-emergent herbicides block new seed
Lawn fertilizing and watering	Lawn	About 1 lb N per 1,000 ft² per feeding; about 1 in water per week	Deep, infrequent early-morning watering	Clippings and leftover fertilizer on pavement wash into streams
Xeriscaping; hydrozoning	Landscape	Water-wise landscaping (Denver Water, 1981); grouping plants by water need	Seven principles: plan and design, improve soil, limit turf, choose suitable plants, efficient irrigation (hydrozones), mulch, maintain	Not "zero-scape" (gravel only); plants still need watering to establish
Rain garden	Landscape	Shallow planted depression that catches roof and pavement runoff	Filters and soaks in stormwater; native plants tolerant of wet and dry	Must drain within a day or two; keep away from foundations

Aquaculture

Aquaculture is the farming of aquatic organisms (fish, shellfish and aquatic plants and algae) under controlled conditions; mariculture is aquaculture in seawater. It now supplies about half of the fish and seafood people eat. The main systems:

Aquaponics couples aquaculture with hydroponics in one recirculating loop. Fish excrete ammonia (through gills and in waste); Nitrosomonas-type bacteria oxidize it to nitrite and Nitrobacter/Nitrospira-type bacteria oxidize that to nitrate; the plants absorb the nitrate as their nitrogen fertilizer and return cleaner water to the fish. Tilapia with lettuce and herbs is the textbook pairing.

The plant side of aquaculture is mostly seaweed farming: nori (Pyropia/Porphyra, a red alga) for sushi wraps; kombu (Saccharina) and wakame (Undaria), brown algae used as food; red algae such as Gracilaria, Gelidium, Kappaphycus and Eucheuma harvested for the gelling agents agar (also the base of microbiology and plant tissue-culture media) and carrageenan; and brown algae as the source of alginate. Freshwater crops include watercress, water spinach, lotus and duckweed (Lemna and Wolffia, fast-growing floating plants used as animal feed). Aquaculture's problems mirror agriculture's: nutrient runoff and eutrophication, disease and antibiotic use, habitat loss (mangroves cleared for shrimp ponds) and dependence on wild-caught fish for feed.

Plant biochemistry

Common lab tests: iodine (starch, blue-black), Benedict's reagent (reducing sugars, brick red when heated), biuret (protein, violet), Sudan stains (lipids), phloroglucinol or safranin (lignin, red).

Pathways plants have and animals lack. The Calvin cycle (carbon fixation); the glyoxylate cycle, which runs in the glyoxysomes of oily germinating seeds and turns fat (via acetyl-CoA) into sugar; the shikimate pathway, which makes the aromatic amino acids phenylalanine, tyrosine and tryptophan (and is the target of glyphosate); the pathway runs from shikimate to chorismate, which branches to tryptophan (via anthranilate) and to prephenate; in plants prephenate is mainly transaminated to arogenate, which arogenate dehydratase turns into phenylalanine and arogenate dehydrogenase into tyrosine; and nitrate and sulfate assimilation (nitrate reductase, nitrite reductase). Phenylalanine feeds the phenylpropanoid pathway to lignin, flavonoids and many other phenolics; tyrosine feeds the benzylisoquinoline alkaloids (morphine, codeine, berberine), betalain pigments, and vitamin E and plastoquinone; tryptophan feeds auxin.

Other biochemistry facts tests ask. Cellulose synthase rosettes in the plasma membrane take UDP-α-glucose from the cytosol and extrude β-1,4 chains straight into the wall (the enzyme inverts the α-linked glucose of UDP-glucose into a β linkage, and in a β-1,4 chain every other glucose is flipped 180°), so straight chains hydrogen-bond side by side into microfibrils; pectin and hemicellulose are made in the Golgi instead and delivered by vesicles. The smooth ER makes lipids and detoxifies drugs and other foreign compounds. Enzymatic browning of cut apples, pears and avocados is caused by polyphenol oxidase (catecholase) oxidizing phenolics; lemon juice (ascorbic acid and acidity) slows it, and the non-browning Arctic apple silences the enzyme. Competitive inhibitors resemble the substrate and bind the active site; noncompetitive inhibitors bind elsewhere and change the enzyme's shape. Fats are first cut into two-carbon acetyl-CoA units by β-oxidation, which in plants runs in peroxisomes and glyoxysomes (not mainly in mitochondria, as in animals) by four repeated steps: oxidation (acyl-CoA oxidase, which makes H₂O₂), hydration, a second oxidation (making NADH) and thiolysis.

Primary metabolites (sugars, amino acids, lipids, nucleotides) are needed by every cell for growth and reproduction; secondary metabolites are not. In agriculture, a crop's primary product is what it is grown for (grain, fiber) and byproducts are useful materials left over from processing (straw, bran, cottonseed oil and meal, bagasse from sugarcane, soybean meal and lecithin). Secondary metabolites are compounds not needed for basic growth, usually used for defense or signaling, and they are the source of most plant drugs:

The flavonoid pathway starts from phenylalanine: phenylalanine ammonia-lyase (PAL) removes ammonia to make cinnamic acid, which is hydroxylated to p-coumaric acid and activated to p-coumaroyl-CoA; chalcone synthase joins it with three malonyl-CoA to make a chalcone, which closes into the flavanone naringenin, the branch point for flavonols (kaempferol, quercetin), anthocyanins and isoflavones. The shikimate pathway itself begins with PEP and erythrose-4-phosphate. Animals cannot make phenylalanine, so people get it from protein foods (meat, fish, eggs, dairy, soy, legumes and nuts) and from the sweetener aspartame, which is why aspartame products carry a warning for people with phenylketonuria. Phytoestrogens are plant compounds that weakly mimic estrogen: isoflavones (genistein and daidzein in soy and red clover), lignans (flaxseed) and coumestans. They are studied for menopausal symptoms, bone health and hormone-related cancers.

Plants in medicine and environmental management

Folk and herbal remedies tests ask about: clove oil (eugenol) is an analgesic and antiseptic used on toothaches, and peppermint oil (menthol) is cooling and mildly numbing; aloe vera gel soothes and moisturizes minor burns and sunburn and reduces inflammation, but it does not undo sun damage or cure the burn; feverfew (containing parthenolide, flavonoids and volatile oils) is used against migraine; evening primrose oil, rich in gamma-linolenic acid, is used for PMS symptoms and eczema (evidence is weak); St. John's wort for mild depression (it speeds the breakdown of many prescription drugs); ginkgo leaf extract, feverfew, garlic and ginger can increase bleeding risk with the blood thinner warfarin; capsaicin from chili peppers in pain creams; echinacea for colds. Onions and garlic (Allium) contain sulfur compounds such as allicin (released when garlic is crushed) that are antimicrobial, and they are studied for modestly lowering blood pressure and cholesterol and for anti-inflammatory flavonoids such as quercetin. Ginseng (Panax) is a traditional Chinese tonic used for fatigue and energy, immunity, blood sugar, memory and digestion. Dandelion leaves and roots are traditional diuretics (its French name, pissenlit, says so), the young leaves are eaten as greens and the roasted root is a coffee substitute. Other common herbal uses: ginger for nausea and motion sickness, milk thistle (silymarin) for the liver, peppermint oil for irritable bowel symptoms, chamomile as a calming tea, valerian for sleep, ginseng as a tonic, turmeric (curcumin) as an anti-inflammatory, senna and psyllium as laxatives, and garlic for cardiovascular health; for most of these the evidence ranges from modest to weak. Herbs have been used in cooking and medicine for thousands of years, in traditions such as Ayurveda (India, about 3,000 years) and traditional Chinese medicine.

Poisonous plants are the flip side of medicinal ones, and many are common ornamentals:

Plants and plant foods dangerous to pets include grapes and raisins (kidney failure in dogs), onions, garlic and chives (red-cell damage in dogs and cats), true lilies and daylilies (kidney failure in cats, even from pollen), sago palm (cycasin, liver failure), chocolate (theobromine), macadamia nuts (weakness and tremors in dogs) and avocado (persin, especially to birds).

Ethnobotany studies how cultures use plants, and many drugs were found by following traditional uses. Pharmacognosy is the study of drugs from natural sources (the term was coined by C. A. Seydler in Analecta Pharmacognostica, 1815). It includes checking crude drug quality against adulteration: deliberate substitution with a substandard or inferior drug (one species passed off as a better one), with an exhausted drug whose active compounds were already extracted, with a superficially similar plant, or with an artificial imitation (sophistication, deliberate faking), and accidental problems such as admixture of other plant parts, confusion over common names, lack of knowledge of the authentic plant, and spoilage in storage.

In environmental management, plants clean, hold and restore land. Phytoremediation uses plants to deal with contamination; plants that take up unusually large amounts of a metal are hyperaccumulators. Harvesting hyperaccumulator shoots to recover and sell the metal (nickel, for example) is called phytomining. Fungi do similar work in mycoremediation: wood-decay (white-rot) fungi break down petroleum hydrocarbons, pesticides and dyes with the same enzymes they use on lignin.

Plants also control erosion (roots binding slopes, fibrous-rooted grasses holding topsoil, cover crops), filter runoff in riparian buffers and constructed wetlands, cool cities and store carbon. Shelterbelts (windbreaks) of trees and shrubs slow the wind across fields, cutting soil erosion and crop water loss, trapping snow and sheltering livestock; the U.S. planted thousands of miles of them across the Great Plains after the Dust Bowl. Desertification is driven by overgrazing, deforestation, poor irrigation that salts the soil, intensive monoculture and drought; diversified farming, cover crops and replanting work against it. Managing invasive species and using prescribed burns in fire-adapted forests are part of the same topic (see Plants in ecosystems).

Importance of plant diversity

Botanists have described roughly 390,000 species of vascular plants (most of them flowering plants), and estimates published by the Royal Botanic Gardens, Kew put roughly two in five at risk of extinction. Diversity matters at three levels: genetic diversity within a species, species diversity within a community, and ecosystem diversity across a landscape. The sum of all the plants and animals of a region is its biota (flora plus fauna).

Genetic diversity lets a species adapt: some individuals carry genes that resist a new disease, pest or climate. Genetic uniformity is the classic risk. The Irish potato famine struck a crop grown largely from a few clonal varieties; the Gros Michel banana was wiped out commercially by Panama disease (a Fusarium wilt), and its Cavendish replacement is now threatened by a new strain, which is why bananas are said to face extinction; in 1970, southern corn leaf blight spread through U.S. maize that shared one susceptible cytoplasm. Crop breeders rely on crop wild relatives and on landraces from Vavilov's centers of origin, the regions where crops were first domesticated.

Diverse plant communities are generally more productive and more stable (David Tilman's long-running grassland experiments at Cedar Creek, Minnesota showed that plots with more species produced more biomass and held their yield steadier through drought), support more pollinators and other wildlife, resist invasion better, and provide ecosystem services: food, medicine, fiber, clean water, soil formation and erosion control, pollinator habitat and climate regulation. Losing diversity means less resilient food supplies, lost sources of future medicines (most plant species have never been screened for drugs), weaker ecosystems and more erosion and flooding.

A biodiversity hotspot (Norman Myers's concept, as defined by Conservation International) is a region with at least 1,500 endemic vascular plant species (found nowhere else) that has lost at least 70% of its original habitat, such as Madagascar, the California Floristic Province and the Cape region of South Africa. Seed banks have a heroic history: during the World War II siege of Leningrad, scientists guarding Vavilov's seed collection starved to death rather than eat the seeds, preserving its genetic diversity. Threats are habitat loss (the biggest), invasive species, pollution, overharvesting and climate change. Conservation is in situ (protecting plants where they grow: reserves, national parks, habitat restoration) or ex situ (outside their habitat: seed banks such as the Svalbard Global Seed Vault, opened in 2008, and Kew's Millennium Seed Bank; botanical gardens; tissue culture and cryopreservation for species whose seeds cannot be dried). International trade in endangered plants such as many orchids and cacti is regulated by CITES.

Botanical vocabulary

The table below is an alphabetical glossary of the morphology, anatomy, life-history and horticulture terms that turn up on Botany tests. Scan the Category column to review a whole family of terms at once (all corolla shapes, all placentation types, all Raunkiær life forms), or look up a single unfamiliar word from a question stem. Each Example is a plant or structure you can picture, which is often exactly what an identification or matching question asks for.

ReferenceBotanical vocabulary· 339 rows

Categories group related terms (Flower, Corolla, Anther, Ovary position, Placentation, Inflorescence, Fruit, Seed, leaf terms, Stem, Root, Bud and twig, Stele, Anatomy, Growth form, Raunkiær life form, Life history, Ecology, Pollination, Dispersal, Reproduction, Horticulture). Synonyms appear in parentheses in the Meaning.

339 rows

Term	Category	Meaning	Example
Accessory fruit	Fruit	Fruit whose flesh comes mainly from tissue other than the ovary, such as receptacle or hypanthium	Strawberry; apple
Achene	Fruit	Dry, indehiscent, one-seeded fruit with the seed attached at one point	"Seeds" on a strawberry; buttercup
Acicular	Leaf shape	Needle-shaped	Pine needles
Actinomorphic	Symmetry	Radially symmetric; divisible into equal halves along several planes	Buttercup; rose
Actinostele	Stele	Protostele whose xylem is star-shaped in cross section, phloem between the arms	Eudicot root; Psilotum stem
Acuminate	Leaf apex	Tapering to a long, drawn-out point	Drip tip of sacred fig (Ficus religiosa)
Acute	Leaf apex	Sharp-pointed with straight sides meeting at less than 90 degrees	Red maple lobe tips
Adnate anther	Anther	Anther attached along its whole length to the filament	Michelia; Ranunculus
Adventitious bud	Bud and twig	Bud arising somewhere other than a leaf axil or shoot tip, such as on a root or leaf	Root suckers of aspen; plantlets on Kalanchoe leaves
Adventitious root	Root	Root arising from a stem or leaf rather than from the radicle	Corn prop roots; roots on a stem cutting
Aerenchyma	Anatomy	Parenchyma with large air spaces that carries oxygen to submerged organs	Water lily petioles; rice roots
Aerial root	Root	Root growing in air, often absorbing moisture or anchoring	Epiphytic orchids; banyan
Aestivation	Flower	Arrangement of sepals or petals in the unopened bud	Twisted in hibiscus; vexillary in pea
Aggregate fruit	Fruit	Fruit formed from many separate carpels of one flower	Raspberry, blackberry (drupelets); magnolia
Albuminous seed	Seed	Mature seed that keeps endosperm as food storage (endospermic)	Corn; castor bean; wheat
Allelopathy	Ecology	Release of chemicals that inhibit nearby plants	Juglone from black walnut
Alternate	Leaf arrangement	One leaf per node	Oak; elm; birch
Androecium	Flower	All the stamens of a flower; the male whorl	Six stamens of a lily
Anemochory	Dispersal	Seed or fruit dispersal by wind	Dandelion pappus; maple samara
Anemophily	Pollination	Wind pollination; flowers small, petal-poor, with lots of light pollen	Corn; grasses; oak; pine
Annual	Life history	Completes its life cycle from seed to seed in one growing season	Corn; marigold; sunflower
Apocarpous	Flower	Carpels of the gynoecium separate from each other	Buttercup; magnolia; strawberry
Apomixis	Reproduction	Production of seeds without fertilization (usually also without meiosis); offspring are clones	Dandelion; many citrus; Kentucky bluegrass
Aril	Seed	Fleshy outgrowth partly or wholly covering a seed, usually from the funiculus	Red cup of yew; mace of nutmeg; lychee flesh
Aristate	Leaf apex	Ending in a bristle or awn	Bristle-tipped lobes of red oak
Atactostele	Stele	Vascular bundles scattered through the ground tissue, no pith-cortex boundary	Corn stem; most monocot stems
Auricle	Leaf part	Small ear-like lobe at the base of a blade; in grasses, where blade meets sheath	Clasping auricles on barley leaves
Autogamy	Pollination	Pollen moves to the stigma of the same flower (self-pollination)	Pea; wheat; tomato
Axile placentation	Placentation	Ovules on a central axis of a compound ovary divided by septa into locules	Tomato; lily; orange
Axillary bud	Bud and twig	Lateral bud in the angle (axil) between a leaf and the stem	Bud above each leaf scar on a twig
Banner	Corolla	Large upper petal of a papilionaceous flower (also standard or vexillum)	Pea; sweet pea
Basal placentation	Placentation	Ovule(s) attached at the base of a one-chambered ovary	Sunflower; buckwheat
Basifixed	Anther	Filament attached to the base of the anther	Brassica; Datura
Berry	Fruit	Fleshy fruit with the entire pericarp soft, usually several seeds	Tomato; grape; blueberry
Biennial	Life history	Grows leaves the first year, flowers and dies the second, usually after winter cold	Carrot; beet; foxglove
Bilabiate	Corolla	Two-lipped corolla, upper and lower lips	Deadnettle (Lamium); sage (Salvia); snapdragon
Bipinnate	Compound leaf	Twice pinnately compound; leaflets borne on secondary rachises	Mimosa tree (Albizia); Kentucky coffeetree
Bolting	Horticulture	Rapid elongation of a flowering stem, often from long days or heat, ruining leafy crops	Lettuce and spinach in summer
Bract	Leaf modification	Reduced or modified leaf associated with a flower or inflorescence	Red "petals" of poinsettia; dogwood white "petals"
Bud scale	Bud and twig	Modified leaf protecting a dormant bud	Overlapping scales on an oak bud
Bud scale scar	Bud and twig	Ring of scars left by terminal bud scales; spacing marks yearly growth	Rings on a buckeye or horse chestnut twig
Bulb	Stem modification	Short underground stem bearing fleshy storage leaves	Onion; tulip; lily
Bundle scar	Bud and twig	Dots in a leaf scar where vascular bundles entered the leaf	Horseshoe-shaped leaf scar of horse chestnut
Campanulate	Corolla	Bell-shaped	Bellflower (Campanula); bluebells
Capitulum	Inflorescence	Head: dense cluster of sessile florets on a flat receptacle, often with an involucre	Sunflower; daisy; dandelion
Capsule	Fruit	Dry dehiscent fruit from a compound ovary (two or more carpels)	Poppy; lily; cotton
Carnivorous plant	Growth form	Plant that traps and digests animals, usually for nitrogen in poor soils	Venus flytrap; pitcher plant; sundew
Carpel	Flower	Ovule-bearing unit of the gynoecium (a modified megasporophyll)	One carpel forms a pea pod
Caruncle	Seed	Spongy outgrowth of the seed coat near the micropyle	Castor bean
Caryopsis	Fruit	Grain: dry one-seeded fruit with the seed coat fused to the pericarp	Corn kernel; wheat; rice
Catkin	Inflorescence	Dangling spike of small unisexual, petal-less flowers (ament)	Willow; birch; male oak flowers
Chamaephyte	Raunkiær life form	Perennating buds on shoots close to the ground (roughly below 25 cm; a few sources use 30 to 50 cm)	Thyme; heather; moss campion
Chilling requirement	Horticulture	Hours of cool temperature a plant needs before buds break or it flowers properly	Apple, peach and blueberry cultivars
Chiropterophily	Pollination	Bat pollination; large pale night-opening flowers, musty odor	Agave; saguaro; baobab
Cladode	Stem modification	Flattened leaf-like stem of one or few internodes (cladophyll)	Asparagus "needles"; butcher's broom
Cleistogamy	Pollination	Self-pollination inside flowers that never open	Violets; henbit; dayflower (Commelina)
Coleoptile	Seed	Protective sheath covering the shoot tip of a grass seedling	Oat and corn seedlings
Complete flower	Flower	Has all four whorls: sepals, petals, stamens, carpels	Lily; rose; cherry
Compound leaf	Compound leaf	Blade divided into separate leaflets on one petiole; bud only at base of whole leaf	Ash; clover; horse chestnut
Compound umbel	Inflorescence	Umbel whose rays each end in a smaller umbel	Carrot; dill; Queen Anne's lace
Coppicing	Horticulture	Cutting trees to the ground repeatedly so they resprout many stems	Willow and hazel coppice
Cordate	Leaf shape	Heart-shaped, with a notch at the base	Redbud; basswood; morning glory
Corm	Stem modification	Short, solid, upright underground stem with thin papery leaves	Gladiolus; crocus; taro
Corona	Flower	Crown-like outgrowth between corolla and stamens	Daffodil trumpet; passionflower filaments
Corymb	Inflorescence	Flat-topped indeterminate cluster; lower pedicels longer	Hawthorn; candytuft
Cotyledon	Seed	Seed leaf of the embryo; one in monocots, two in eudicots	Two halves of a bean seed
Crenate	Leaf margin	Margin with rounded, scalloped teeth	Kalanchoe pinnata; ground ivy
Cruciform	Corolla	Four petals arranged in a cross	Mustard; cabbage; radish
Cryptophyte	Raunkiær life form	Perennating buds below ground or under water; includes geophytes, helophytes, hydrophytes	Tulip; cattail; water lily
Culm	Stem	Jointed stem of a grass or sedge	Bamboo cane; wheat straw
Cultivar	Horticulture	Cultivated variety selected and kept for its traits; written in single quotes	Malus domestica 'Honeycrisp'
Cuneate	Leaf base	Wedge-shaped, tapering to a point at the base	Ginkgo fan
Cutting	Horticulture	Piece of stem, leaf or root rooted to make a new plant; softwood (new spring growth) or hardwood (dormant mature wood)	Coleus or willow stem cuttings
Cyathium	Inflorescence	Cup of bracts holding one naked female flower and many reduced male flowers	Poinsettia (Euphorbia)
Cyme	Inflorescence	Determinate cluster; the terminal (central) flower opens first	Chickweed; Sweet William
Cypsela	Fruit	Achene-like fruit from an inferior ovary, often topped by a pappus	Sunflower "seed"; dandelion
Damping-off	Horticulture	Seedling collapse at the soil line caused by soil fungi and oomycetes	Pythium on seedling trays
Deciduous	Life history	Sheds all leaves for part of the year	Maple; oak; larch (a deciduous conifer)
Decumbent	Habit	Lying on the ground but with the tip turned upward	Purslane; many clovers
Decussate	Leaf arrangement	Opposite pairs, each pair at right angles to the next	Mint; coleus
Dehiscent	Fruit	Splitting open at maturity to release seeds	Pea pod; milkweed follicle
Deltoid	Leaf shape	Triangular	Eastern cottonwood (Populus deltoides)
Dentate	Leaf margin	Teeth pointing outward, perpendicular to the margin	Arrowwood viburnum (Viburnum dentatum)
Determinate growth	Horticulture	Shoot ends in a flower cluster and stops elongating; fruit ripens over a short span	Bush (determinate) tomatoes
Determinate inflorescence	Inflorescence	Main axis ends in a flower; flowers open from the top or center outward	Cymes of chickweed
Diadelphous	Anther	Stamens joined by filaments into two groups, typically 9 + 1	Pea; bean
Dichogamy	Reproduction	Male and female parts of a flower mature at different times	Protandrous sunflower; protogynous magnolia
Dichotomous venation	Venation	Veins fork repeatedly in pairs, no cross-connections	Ginkgo; maidenhair fern
Dictyostele	Stele	Siphonostele broken into a net of strands by many overlapping leaf gaps	Many fern rhizomes
Didynamous	Anther	Four stamens, two long and two short	Deadnettle (Lamium); snapdragon
Dioecious	Reproduction	Male and female flowers (or cones) on separate plants	Holly; ginkgo; asparagus; date palm
Distichous	Leaf arrangement	Leaves in two vertical rows on opposite sides of the stem	Grasses; elm; iris
Division	Horticulture	Splitting a clump into rooted pieces to propagate it	Hosta; daylily; iris rhizomes
Dorsifixed	Anther	Filament attached to the back of the anther, anther fixed	Passiflora
Doubly serrate	Leaf margin	Large teeth themselves bearing smaller teeth	Birch; American elm
Drupe	Fruit	Fleshy fruit with one seed inside a stony endocarp (pit)	Peach; cherry; olive
Elaiosome	Seed	Fat-rich appendage on a seed that attracts ants	Trillium; bloodroot; violets
Elliptic	Leaf shape	Widest at the middle, tapering equally to both ends	Flowering dogwood
Emarginate	Leaf apex	Shallowly notched at the tip	Boxwood
Endosperm	Seed	Food-storing tissue of angiosperm seeds, usually triploid	Coconut water and meat; popcorn starch
Entire	Leaf margin	Smooth margin without teeth or lobes	Magnolia; lilac
Entomophily	Pollination	Insect pollination; colorful, scented flowers with nectar	Apple; sunflower; clover
Ephemeral	Life history	Very short-lived plant, or one with a brief above-ground season	Desert annuals; spring ephemerals like trout lily
Epicotyl	Seed	Embryonic stem above the cotyledons	Hooked shoot of a pea seedling
Epigeal germination	Seed	Hypocotyl elongates and lifts the cotyledons above the soil	Common bean; sunflower
Epigynous	Ovary position	Floral parts attached at the top of an inferior ovary	Apple; squash; sunflower
Epipetalous	Anther	Stamens attached to the petals or corolla tube	Morning glory; mint; tomato
Epiphyte	Growth form	Grows on another plant for support only, not as a parasite	Spanish moss; many orchids and bromeliads
Espalier	Horticulture	Training a tree or shrub flat against a wall or frame	Espaliered apple and pear
Etiolation	Horticulture	Pale, spindly, long-internode growth in darkness or low light	Seedlings on a dim windowsill
Eustele	Stele	Discrete collateral vascular bundles in a ring around a pith	Sunflower and other eudicot stems; conifers
Evergreen	Life history	Keeps green leaves year round, shedding them gradually	Pine; holly; rhododendron
Exalbuminous seed	Seed	Mature seed with no endosperm left; food stored in cotyledons	Bean; pea; peanut
F1 hybrid	Horticulture	First-generation cross of two inbred parents; uniform and vigorous; seed does not breed true	Most modern sweet corn
Fascicle	Leaf part	Bundle of conifer needles held in a basal sheath	Five needles in eastern white pine; two in red pine
Fibrous root system	Root	Many similar-sized roots from the stem base, no dominant taproot	Grasses; corn; onion
Floret	Flower	Small individual flower in a dense cluster	Florets of a sunflower head or grass spikelet
Follicle	Fruit	Dry fruit from one carpel that splits along one seam	Milkweed; peony; columbine
Forb	Growth form	Broad-leaved herbaceous plant that is not a grass, sedge or rush	Clover; aster; goldenrod
Free-central placentation	Placentation	Ovules on a free-standing central column in a one-chambered ovary	Carnation; primrose
Funnelform	Corolla	Tube widening gradually into a flaring limb (infundibuliform)	Morning glory; petunia
Gamopetalous	Corolla	Petals fused into a tube (sympetalous)	Morning glory; petunia
Geitonogamy	Pollination	Pollen from another flower on the same plant; genetically selfing	Flowers on one corn plant
Geophyte	Raunkiær life form	Perennates by underground buds on bulbs, corms, tubers or rhizomes	Tulip; crocus; potato
Glabrous	Leaf surface	Smooth, without hairs	Upper surface of a magnolia leaf
Glandular	Leaf surface	Bearing secretory hairs or glands, often sticky	Petunia; tobacco; sundew tentacles
Glaucous	Leaf surface	Covered with a whitish or bluish waxy bloom that rubs off	Blue spruce; cabbage; plum skin
Grafting	Horticulture	Joining a scion to a rootstock so the vascular cambia unite	Apple cultivars on dwarfing rootstocks
Graminoid	Growth form	Grass-like plant: grasses, sedges, rushes	Bluestem; sedges
Gynoecium	Flower	All the carpels of a flower; the female whorl	Pistils in the center of a buttercup
Halophyte	Ecology	Plant adapted to salty soil or water	Pickleweed (Salicornia); mangroves
Hardening off	Horticulture	Gradually exposing transplants to outdoor conditions	Moving seedlings outside a few hours a day
Hardiness zone	Horticulture	USDA map zone based on average annual extreme minimum temperature	Zone 5 vs. zone 9
Hastate	Leaf shape	Arrowhead-shaped with basal lobes pointing outward	Sheep sorrel (Rumex acetosella)
Haustorium	Root	Absorptive organ a parasite inserts into host tissue	Dodder; mistletoe
Heartwood	Anatomy	Inner, dead, darker secondary xylem that no longer conducts water	Dark center of black walnut lumber
Helophyte	Raunkiær life form	Marsh plant with buds in waterlogged soil and shoots above water	Cattail; arrowhead
Hemicryptophyte	Raunkiær life form	Perennating buds at the soil surface, often protected by litter or snow	Dandelion; many grasses
Hemiparasite	Growth form	Parasite that photosynthesizes but takes water and minerals from a host	Mistletoe; Indian paintbrush
Herbaceous	Stem	Non-woody; above-ground stems die back after the season	Basil; hosta; peony
Hesperidium	Fruit	Berry with a leathery oil-dotted rind and juice sacs in segments	Orange; lemon
Heterophylly	Leaf part	Different leaf shapes on the same plant	Sassafras; juvenile vs. adult English ivy
Heterostyly	Reproduction	Flowers of different plants have different style and stamen lengths, promoting outcrossing	Primrose (pin and thrum); buckwheat
Hilum	Seed	Scar on a seed where the funiculus was attached	"Eye" of a black-eyed pea
Hirsute	Leaf surface	Covered in coarse, rather stiff hairs	Stems of many sunflowers
Holoparasite	Growth form	Parasite without chlorophyll, wholly dependent on its host	Dodder; Rafflesia; broomrape
Hydrochory	Dispersal	Dispersal by water	Coconut; water lily seeds
Hydrophyte	Ecology	Plant growing in water or waterlogged soil	Water lily; duckweed; pondweed
Hypanthium	Flower	Floral cup formed from the fused bases of sepals, petals and stamens	Cherry; rose; fleshy part of apple
Hypocotyl	Seed	Embryonic stem between cotyledons and radicle	Hook of a bean seedling
Hypogeal germination	Seed	Epicotyl elongates and cotyledons stay below ground	Pea; corn; oak
Hypogynous	Ovary position	Sepals, petals and stamens attached below a superior ovary	Buttercup; tomato; mustard
Imperfect flower	Flower	Unisexual flower: stamens or carpels but not both	Corn tassel and ear flowers; squash
Incomplete flower	Flower	Missing one or more of the four floral whorls	Grass flowers; any unisexual flower
Indehiscent	Fruit	Not splitting open at maturity	Acorn; achene; samara
Indeterminate growth	Horticulture	Shoot keeps elongating and flowering until killed by frost	Vining (indeterminate) tomatoes; pole beans
Indeterminate inflorescence	Inflorescence	Main axis keeps growing; flowers open from the base or edge inward	Raceme of lupine; spike of gladiolus
Inferior ovary	Ovary position	Ovary below the attachment of sepals, petals and stamens	Apple; squash; banana; daffodil
Intercalary meristem	Anatomy	Meristem at the base of internodes or leaves	Grass stems and leaves regrow after mowing
Involucre	Inflorescence	Whorl of bracts below an inflorescence	Green bracts under a sunflower head
Keel	Corolla	Two lower fused petals enclosing stamens and pistil in a papilionaceous flower	Pea; lupine
Lanceolate	Leaf shape	Lance-shaped; long, widest below the middle, tapering to the tip	Willow; peach
Laticifer	Anatomy	Cell or tube that holds latex	Milkweed; rubber tree; opium poppy
Layering	Horticulture	Rooting a stem while still attached to the parent plant	Air layering of rubber plant; tip layering of blackberry
Leaf scar	Bud and twig	Scar on a twig where a leaf petiole was attached	Large shield-shaped scars on ailanthus
Legume	Fruit	Dry fruit from one carpel splitting along two seams	Pea; bean; peanut (indehiscent)
Lenticel	Stem	Raised pore in bark or periderm allowing gas exchange	Horizontal marks on cherry and birch bark
Liana	Growth form	Woody climbing vine rooted in the ground	Wild grape; poison ivy vines; wisteria
Ligulate	Corolla	Strap-shaped corolla	Ray florets; dandelion florets
Ligule	Leaf part	Membrane or hair fringe where a grass blade meets the sheath	Grass leaf collar
Linear	Leaf shape	Long and narrow with nearly parallel sides	Grasses; daylily
Loment	Fruit	Legume constricted between seeds that breaks into one-seeded pieces	Tick trefoil (Desmodium)
Marcescent	Life history	Dead leaves that stay on the plant through winter	Young oak and American beech
Marginal placentation	Placentation	Ovules along one suture of a single-carpel ovary	Pea; bean
Mesophyll	Anatomy	Leaf photosynthetic tissue; palisade and spongy layers	Leaf cross section
Micropyle	Seed	Small opening in the integuments where the pollen tube enters; later a pore in the seed coat	Pore next to a bean's hilum
Mixed bud	Bud and twig	Bud containing both leaves and flowers	Apple spur buds
Monadelphous	Anther	Stamens joined by filaments into a single tube	Hibiscus; hollyhock
Monocarpic	Life history	Flowers and fruits once, then dies (semelparous)	Agave (century plant); bamboo; annuals
Monoecious	Reproduction	Separate male and female flowers on the same plant	Corn; squash; oak; birch
Mucronate	Leaf apex	Ending in a short, abrupt point	Alfalfa leaflets
Multiple fruit	Fruit	Fruit formed from the ovaries of many flowers fused together	Pineapple; mulberry; fig
Mycoheterotroph	Growth form	Non-green plant that gets carbon from mycorrhizal fungi	Indian pipe (Monotropa)
Mycorrhiza	Root	Mutualism between fungus and root aiding mineral (especially P) uptake	Ectomycorrhizae on pine; arbuscular on corn
Myrmecochory	Dispersal	Seed dispersal by ants	Trillium; bloodroot
Naked bud	Bud and twig	Bud without protective scales	Pawpaw; witch hazel
Nut	Fruit	Hard, dry, indehiscent fruit, usually one seed, from a compound ovary	Acorn; hazelnut; chestnut
Obcordate	Leaf shape	Inverted heart shape, notch at the tip	Wood sorrel (Oxalis) leaflets
Oblique	Leaf base	Sides of the base unequal	American elm; hackberry; basswood
Oblong	Leaf shape	Longer than wide with nearly parallel sides	Banana
Obovate	Leaf shape	Egg-shaped with the broad end at the tip	Pawpaw; many magnolias
Ocrea	Leaf part	Sheath around the stem formed from fused stipules	Knotweed; rhubarb; buckwheat
Odd-pinnate	Compound leaf	Pinnately compound with a terminal leaflet (imparipinnate)	Ash; rose; sumac
Open-pollinated	Horticulture	Pollinated naturally; seed grows true to type if isolated	Heirloom beans and tomatoes
Opposite	Leaf arrangement	Two leaves per node on opposite sides	Maple; ash; dogwood; horse chestnut
Orbicular	Leaf shape	Nearly circular	Nasturtium
Ovate	Leaf shape	Egg-shaped, broadest below the middle	Hibiscus; lilac
Ovule	Seed	Megasporangium with integuments; becomes the seed after fertilization	Ovules inside a pea flower's ovary
Palmate venation	Venation	Several major veins radiate from the base	Maple; sycamore
Palmately compound	Compound leaf	Leaflets radiate from the petiole tip	Horse chestnut; buckeye; Virginia creeper
Palmately lobed	Leaf shape	Lobes radiating from a common point	Maple; sweetgum
Panicle	Inflorescence	Branched raceme; compound indeterminate cluster	Oat; rice; yucca
Papilionaceous	Corolla	Butterfly-like corolla with banner, two wings and a keel	Pea; bean; clover
Pappus	Flower	Modified calyx of bristles, hairs or scales on Asteraceae fruits	Dandelion "parachute"
Parallel venation	Venation	Main veins run side by side along the blade	Grasses; corn; lily
Parietal placentation	Placentation	Ovules on the inner wall of a one-chambered compound ovary	Violet; papaya; mustard
Parthenocarpy	Reproduction	Fruit development without fertilization, giving seedless fruit	Banana; navel orange; seedless cucumber
Pedicel	Inflorescence	Stalk of a single flower in an inflorescence	Stalk of each cherry
Peduncle	Inflorescence	Stalk of a whole inflorescence or a solitary flower	Stalk of a sunflower head
Peltate	Leaf shape	Petiole attached to the underside of the blade, not the margin	Nasturtium; lotus; mayapple
Pepo	Fruit	Berry with a hard rind, from an inferior ovary	Pumpkin; cucumber; watermelon
Perennial	Life history	Lives more than two years	Hosta; oak; asparagus
Perfect flower	Flower	Has both stamens and carpels (bisexual)	Lily; rose; tomato
Perfoliate	Leaf base	Leaf base surrounding the stem so the stem seems to pierce it	Perfoliate bellwort; boneset (connate-perfoliate)
Perianth	Flower	Calyx and corolla together, or all the tepals	Six tepals of a tulip
Pericarp	Fruit	Fruit wall developed from the ovary wall: exocarp, mesocarp, endocarp	Peel, flesh and pit of a peach
Perigynous	Ovary position	Floral parts on the rim of a hypanthium around a free, superior ovary	Cherry; plum; rose
Perisperm	Seed	Food storage tissue derived from the nucellus	Beet; black pepper
Phanerophyte	Raunkiær life form	Perennating buds on shoots well above the ground	Trees and shrubs
Phellogen	Anatomy	Cork cambium; produces cork outward and phelloderm inward	Source of commercial cork in cork oak
Phyllary	Inflorescence	Single bract of the involucre of an Asteraceae head	Spiny phyllaries of thistles and artichoke
Phylloclade	Stem modification	Flattened green stem of several internodes doing photosynthesis	Prickly pear (Opuntia) pads; Christmas cactus
Phyllode	Leaf modification	Flattened petiole that functions as a leaf blade	Australian acacias
Phyllotaxy	Leaf arrangement	Arrangement of leaves on a stem; spiral often near 137.5 degrees	Sunflower; pine cone spirals
Pinching	Horticulture	Removing a shoot tip to break apical dominance and promote branching	Basil; chrysanthemum; fuchsia
Pinnate venation	Venation	Lateral veins branch from one midrib like a feather	Elm; beech; cherry
Pinnately compound	Compound leaf	Leaflets arranged on both sides of a rachis	Ash; walnut; rose
Pinnately lobed	Leaf shape	Lobes arranged along both sides of a midrib	White oak
Pistil	Flower	Stigma, style and ovary; one carpel or several fused carpels	Pistil in the center of a lily
Pistillate	Flower	Bearing only carpels (female)	Corn ear; female holly flowers
Placentation	Placentation	Arrangement of placentas (ovule-bearing tissue) and their ovules within an ovary	Axile in tomato; parietal in violet
Plectostele	Stele	Protostele with xylem in parallel plates	Lycopodium (club moss) stems
Plumule	Seed	Embryonic shoot tip above the cotyledons	Tiny leaves inside a bean seed
Pneumatophore	Root	Root growing upward out of mud or water to take in air	Black mangrove; bald cypress knees (function debated)
Pollinium	Flower	Mass of pollen grains moved as a single unit	Milkweed; orchids
Polyembryony	Seed	More than one embryo in one seed	Citrus; mango
Polypetalous	Corolla	Petals separate (choripetalous)	Rose; buttercup
Pome	Fruit	Accessory fruit whose flesh is the hypanthium around a papery core	Apple; pear; quince
Poricidal	Anther	Opening through pores, used for anthers and capsules	Blueberry and eggplant anthers (buzz pollination); poppy capsule
Prickle	Stem modification	Sharp outgrowth of epidermis or cortex, not a leaf or stem	Rose; raspberry
Prop root	Root	Adventitious root from the lower stem that braces the plant	Corn; red mangrove
Protandry	Reproduction	Anthers shed pollen before the stigma of the same flower is receptive	Sunflower; carrot; Campanula
Protogyny	Reproduction	Stigma receptive before the same flower's anthers shed pollen	Magnolia; plantain (Plantago)
Protostele	Stele	Solid central core of xylem surrounded by phloem, no pith	Roots; Rhynia; club mosses
Pseudoterminal bud	Bud and twig	Uppermost lateral bud that acts as terminal after the shoot tip aborts	Elm; basswood
Pubescent	Leaf surface	Covered with short, soft hairs	Peach fruit skin; African violet leaves
Raceme	Inflorescence	Unbranched indeterminate axis with stalked flowers	Snapdragon; lupine; foxglove
Rachis	Compound leaf	Main axis of a pinnately compound leaf or inflorescence	Midline of an ash leaf
Radicle	Seed	Embryonic root; first structure out of a germinating seed	Emerging tip of a sprouting bean
Ray floret	Flower	Strap-shaped floret at the edge of a composite head	Yellow "petals" of a sunflower
Recalcitrant seed	Seed	Seed killed by drying, so it cannot be stored long (opposite: orthodox seeds like wheat and bean)	Avocado; cacao; oak acorns
Receptacle	Flower	Tip of the flower stalk bearing the floral parts	Red flesh of a strawberry
Reniform	Leaf shape	Kidney-shaped	Wild ginger (Asarum)
Reticulate venation	Venation	Veins forming a branching network (netted)	Most eudicots; maple; oak
Revolute	Leaf margin	Margin rolled under toward the lower surface	Rosemary
Rhizome	Stem modification	Horizontal underground stem with nodes and scale leaves	Iris; ginger; bamboo
Root nodule	Root	Swelling that houses nitrogen-fixing bacteria	Rhizobium nodules on pea and clover roots (Bradyrhizobium on soybean)
Rootstock	Horticulture	Lower part of a graft providing roots	M9 dwarfing apple rootstock
Rosette	Leaf arrangement	Cluster of leaves crowded at the stem base	Dandelion; lettuce; first-year carrot
Rotate	Corolla	Wheel-shaped; short tube with flat spreading lobes	Tomato; potato
Sagittate	Leaf shape	Arrowhead-shaped with basal lobes pointing backward	Arrowhead (Sagittaria)
Salverform	Corolla	Slender tube that abruptly flares into a flat limb	Phlox; periwinkle
Samara	Fruit	Dry indehiscent fruit with a wing	Maple (double samara); ash; elm
Sapwood	Anatomy	Outer, lighter, water-conducting secondary xylem	Pale outer wood of a log
Scabrous	Leaf surface	Rough to the touch like sandpaper	Common sunflower leaves
Scape	Inflorescence	Leafless flowering stalk rising from ground level	Dandelion; onion; daylily
Scarification	Horticulture	Breaking or softening a hard seed coat to allow water uptake	Nicking morning glory or lupine seeds
Schizocarp	Fruit	Dry fruit from a compound ovary that splits into one-seeded mericarps	Carrot; maple; mallow
Scion	Horticulture	Upper part of a graft that becomes the shoot	'Gala' apple scion
Sclereid	Anatomy	Short, irregular sclerenchyma cell with a thick lignified wall (stone cell)	Grit in pear flesh; nut shells
Scutellum	Seed	Single cotyledon of a grass embryo that absorbs endosperm food	Corn kernel embryo
Serrate	Leaf margin	Sharp, saw-like teeth pointing toward the tip	Black cherry; peach
Sheath	Leaf part	Leaf base wrapping around the stem	Grass and corn leaf sheaths
Silicle	Fruit	Short silique, about as long as wide	Shepherd's purse; money plant (Lunaria)
Silique	Fruit	Long dry fruit of two carpels whose valves split away from a persistent replum and central partition (septum)	Mustard; radish; Arabidopsis
Simple fruit	Fruit	Fruit from a single ovary of a single flower	Peach; tomato; bean pod
Simple leaf	Leaf part	Blade in one piece, even if lobed	Oak; maple
Siphonostele	Stele	Stele with a central pith surrounded by a cylinder of vascular tissue	Many fern rhizomes; horsetails
Solenostele	Stele	Siphonostele with phloem both inside and outside the xylem and widely spaced leaf gaps	Some fern rhizomes (Marsilea)
Sorosis	Fruit	Multiple fruit from a fleshy spike or catkin of flowers	Pineapple; mulberry
Spadix	Inflorescence	Fleshy spike of tiny flowers, usually with a spathe	Jack-in-the-pulpit; Anthurium; calla lily
Spathe	Leaf modification	Large bract enclosing or subtending a spadix	White "flower" of calla lily
Spike	Inflorescence	Unbranched indeterminate axis with sessile flowers	Plantain (Plantago); gladiolus; wheat (compound)
Spikelet	Inflorescence	Basic grass flower unit: florets on a small axis above two empty bracts (glumes); each floret enclosed by a lemma and palea	Spikelets of wheat
Spine	Leaf modification	Sharp, hard modified leaf or stipule	Cactus spines; barberry
Spinose	Leaf margin	Margin with sharp spines	American holly
Spring ephemeral	Ecology	Woodland herb that grows and flowers before the canopy leafs out	Trillium; spring beauty; bloodroot
Spur	Bud and twig	Short shoot with crowded nodes, often fruit-bearing; also a hollow nectar sac on a flower	Apple spurs; columbine petal spurs
Stamen	Flower	Male organ: anther on a filament	Six stamens of a lily
Staminate	Flower	Bearing only stamens (male)	Corn tassel; male birch catkins
Stele	Stele	Central vascular cylinder of a stem or root, with pericycle and pith if present	Root stele inside the endodermis
Stem tendril	Stem modification	Modified stem that coils around supports	Grape; passionflower
Stipule	Leaf part	Small leaf-like appendage at the base of a petiole	Large stipules of pea; rose stipules
Stipule scar	Bud and twig	Scar left by a fallen stipule; may encircle the twig	Ring around tulip tree and magnolia twigs
Stolon	Stem modification	Horizontal stem along the surface rooting at nodes	Strawberry; bermudagrass
Storage root	Root	Root thickened with stored food	Sweet potato; dahlia; carrot
Stratification	Horticulture	Holding seeds cold and moist to break dormancy	Apple and maple seeds
Subshrub	Growth form	Plant woody only at the base, with herbaceous upper stems	Lavender; thyme
Succulent	Growth form	Plant with thick fleshy water-storing leaves or stems	Aloe; jade plant; cacti
Sucker	Stem modification	Shoot arising from a root or the base of the plant	Red raspberry; lilac; sumac
Superior ovary	Ovary position	Ovary above the attachment of sepals, petals and stamens	Tomato; lily; pea
Syconium	Fruit	Multiple fruit from a hollow receptacle lined with flowers	Fig
Syncarpous	Flower	Carpels fused into one compound pistil	Tomato; lily; orange
Syngenesious	Anther	Anthers fused into a tube, filaments free	Sunflower; daisy (Asteraceae)
Taproot	Root	Dominant main root from the radicle, with smaller laterals	Carrot; dandelion; oak seedling
Tendril	Leaf modification	Slender coiling organ for climbing; may be modified leaf, leaflet or stem	Pea leaflet tendrils
Tepal	Flower	Perianth part not distinguished as sepal or petal	Tulip; lily
Terminal bud	Bud and twig	Bud at the tip of a twig	Large terminal bud of horse chestnut
Tetradynamous	Anther	Six stamens, four long and two short	Mustard family (Brassicaceae)
Therophyte	Raunkiær life form	Annual that survives the bad season only as seed	Sunflower; corn; desert annuals
Thorn	Stem modification	Sharp modified stem (branch) arising from an axillary bud	Hawthorn; honey locust; citrus
Tiller	Stem	Shoot from the base of a grass plant	Tillers of wheat and rice
Tissue culture	Horticulture	Growing plants from cells or tissues on sterile nutrient media (micropropagation)	Orchids; banana plantlets
Tomentose	Leaf surface	Densely covered in matted, woolly hairs	Mullein; lamb's ear
Trichome	Leaf surface	Hair or other epidermal outgrowth	Stinging hairs of nettle; cotton fibers
Trifoliate	Compound leaf	Compound leaf of three leaflets (trifoliolate)	Clover; poison ivy; bean
Trimerous	Flower	Floral parts in threes or multiples of three; typical of monocots (eudicots: fours or fives)	Lily; tulip; trillium
Truncate	Leaf apex	Squared off as if cut straight across	Tulip tree
Tuber	Stem modification	Swollen tip of an underground stem storing food; eyes are nodes	Potato; Jerusalem artichoke
Tuberous root	Root	Swollen root storing food, without nodes or eyes	Sweet potato; dahlia
Tubular	Corolla	Corolla a long narrow tube	Trumpet creeper; disk florets
Twining	Habit	Climbing by spiraling the stem around a support	Morning glory; pole bean; wisteria
Tylosis	Anatomy	Outgrowth of parenchyma into a vessel that plugs it	White oak (why it holds wine and whiskey)
Umbel	Inflorescence	Flower stalks all arise from one point at the top of the peduncle	Onion; milkweed; carrot (compound umbel)
Undulate	Leaf margin	Margin wavy up and down	Curly dock (Rumex crispus)
Unifoliolate	Compound leaf	Compound leaf reduced to one leaflet, with a joint between it and the petiole	Citrus (winged petiole)
Urceolate	Corolla	Urn-shaped, constricted at the mouth	Blueberry; heath
Vascular bundle	Anatomy	Strand of xylem and phloem	Veins of a leaf; strings in celery
Vascular cambium	Anatomy	Lateral meristem making secondary xylem inward and phloem outward	Layer under a tree's bark
Velamen	Root	Spongy multilayer epidermis of aerial roots that absorbs water	Epiphytic orchid roots
Versatile anther	Anther	Anther attached at a midpoint so it swings freely on the filament	Grasses; lily
Verticillaster	Inflorescence	False whorl of paired cymes at each node	Mint; sage (Salvia)
Vivipary	Seed	Seed germinating while still attached to the parent	Red mangrove; sprouting kernels on an ear of corn
Whorled	Leaf arrangement	Three or more leaves at a node	Catalpa (often 3); bedstraw (Galium)
Winter annual	Life history	Germinates in fall, overwinters as a seedling, flowers and dies in spring	Winter wheat; henbit; chickweed
Xenogamy	Pollination	Cross-pollination between flowers on different plants	Apple orchards need pollinizer cultivars
Xerophyte	Ecology	Plant adapted to dry habitats, such as with thick cuticle or sunken stomata	Cacti; oleander
Zoochory	Dispersal	Seed dispersal by animals, inside them or stuck to them	Burdock burs; cherries eaten by birds
Zygomorphic	Symmetry	Bilaterally symmetric; only one plane divides it into mirror halves	Orchid; pea; snapdragon

Common pitfalls

How tournaments test this

The archive holds 2,018 Botany questions from public tests across seven seasons (2019-20 through 2025-26). The site's practice bank holds 2,866 Botany questions, and most of them are not in the archive: about 1,150 are exported from or match archive tests, and about 1,650 come from other invitational tests that the archive does not have. Those tests were written to several different topic lists, so use them for style and for the topics that overlap with 2027, not as a map of the 2027 outline.

• What the bank asks most. Sorting the bank questions that fit the 2027 outline by main topic gives roughly: horticulture and aquaculture 11%, photosynthesis 10%, plant groups and life cycles 9%, hormones, tropisms and germination 6%, flowers, fruits and seeds 6%, ecology and adaptations 6%, roots, stems and leaves 5.5%, transport 5%, diseases and deficiencies 5%, reproduction 4%, nutrient cycles and soil 4%, crops and plant products 4%, GMOs 3%, taxonomy and identification 3%, tissues 3%, and smaller shares for cells, paleobotany, growth, medicine, biochemistry, genetics, monocots vs. dicots, history and calculations. Horticulture is heavy because many invitationals wrote practical gardening questions (propagation, pruning, fertilizer math, soil).
• Division split. Division B accounts for 1,104 archived questions (55%), Division C for 868 (43%), and 46 are shared.
• Question types. Multiple choice 45.8% (925), free response 40.2% (812), true/false 7.5% (151), select-all 5.5% (111), numeric 0.8% (16), matching 0.1% (3). Free response is common, so practice writing short, exact answers.
• Task profile. "Which of the following" leads (11.8%), then "explain or why" (4.9%), definitions (2.2%), identifying a structure in a figure (2.0%) and calculations (1.8%). With supervisors supplying specimens, slides and microscopes, figure and specimen identification is likely to grow at station-format tournaments.
• Subtopic tags (a question can carry several): Plant Anatomy 32%, Plant Physiology 21%, Reproduction 19%, Ecology 14%, Classification 14%, Photosynthesis 13%, Genetics 8%, Plant Nutrition 7%.
• Topics that match the 2027 additions. History, medicinal plants, GMOs and plant disease all appear in the archive already, mostly in 2020-21 and 2021-22 invitationals (Theophrastus is the official key to 11 questions; Bt proteins, quinine and Rauvolfia, and crop viruses all recur). Paleobotany, algae, nutrient deficiencies and the Division C additions are thinner in the archive, so build those from the references below.
• Concentration. The CrabSO Invitational (MD, 2026) supplies 229 questions (about 11%) and the UT Austin MiniSO Invitational (2021) 203, so a few writers shape the archive's style.
• Recurring concepts (archive and bank prompts containing the term): "plant cells" (65), Calvin cycle (64), CAM plants (41), vascular plants (36), double fertilization (29), cell wall (28), life cycle (27), genetically modified (24), land plants (24), genetic engineering (20), carbon fixation (19), seed germination (19), guard cells (18), nitrogen cycle (17), turgor pressure (16).
• Most common correct answers: phloem (22), xylem (21), abscisic acid (17), C₄ plants (16), auxin (14), CAM plants (14), cytokinin (14), calcium (13), ethylene (13), photosynthesis (11), Theophrastus (11).

Strategy

• Split the outline, then cross-check. One partner owns structure, growth, transport, photosynthesis and the plant groups; the other owns history, paleobotany, genetics, ecology, crops, GMOs and disease (plus, in Division C, horticulture, biochemistry, medicine and diversity). Swap and check each other's answers in the last 10 to 15 minutes.
• Prepare for both formats. The supervisor picks a paper test or stations. For stations, practice on a timer, identify structures from photos and slides, and use a compound microscope until focusing at high power is quick.
• Use the sheet for what you cannot derive. History dates and names, the paleobotany timeline, the deficiency table with mobility, the hormone table, the pathogen table, the group comparison and monocot-dicot tables, the drug-source table (Division C), and the water-potential, transpiration and NPP formulas. Leave out things you can reason through, such as the logic of the disease triangle.
• Show work in calculations. Formula, numbers with units, answer with appropriate significant figures. Rounding rules: multiply or divide to the fewest significant figures; add or subtract to the fewest decimal places; exact counts do not limit precision.
• Answer free response with mechanism. "Older leaves yellow first because nitrogen is mobile and is moved to new growth" earns more than "nitrogen deficiency".
• Two Class II calculators. Bring two identical scientific calculators so both partners can compute at once.

Test yourself

These questions come from public tournament tests in the archive and fall inside the 2027 outline. Each uses an official-key answer; the notes explain the reasoning where it is not obvious. Each question links to its full test.

Test yourselfPlant body, transport, photosynthesis and the major plant groups

0 / 0 correct

1. 1

   Which of the following is true regarding vascular cambium? Select all that apply

   Question 1 options

   AIt produces secondary xylem and phloemBIt produces a fruitCIt is directly responsible for producing a sweet, sugary sapDIt increases the diameter of stems and rootsEIt produces showy flowers
   Check answer

   From: CrabSO Satellite Invitational, 2024-25, Division B

2 questions from this set are no longer available.

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Test yourselfHistory, genetics and reproduction

0 / 0 correct

1. 1

   Who is known as the father of botany?

   Question 1 options

   APedanius DioscoridesBAristotleCTheophrastusDCatoEVarro

   From: UChicago Invitational, 2021-22, Division C

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Test yourselfCycles, crops, GMOs, disease and medicine

0 / 0 correct

1. 1

   What process of the nitrogen cycle do the bacteria associated with legumes take part in?

   Question 1 options

   ADenitrificationBNitrogen FixationCAmmonificationDNitrification

   From: UChicago Invitational, 2021-22, Division C

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References and further reading

• Science Olympiad event pages, the 2027 Botany rules (Division B page B11, Division C page C13) and the General Rules: https://www.soinc.org
• OpenStax, Biology 2e, chapters on seedless and seed plants, plant form and physiology, and photosynthesis (free online): https://openstax.org/details/books/biology-2e
• Raven, P. H., Evert, R. F. and Eichhorn, S. E., Biology of Plants (W. H. Freeman): standard reference for anatomy, physiology, plant groups and evolution.
• Taiz, L., Zeiger, E. et al., Plant Physiology and Development (Sinauer/Oxford): water potential, mineral nutrition, deficiency symptoms and hormones.
• Agrios, G. N., Plant Pathology (Academic Press): the disease triangle and pathogen groups.
• American Phytopathological Society, Education Center (introductions to plant diseases): https://www.apsnet.org/edcenter
• Royal Botanic Gardens, Kew, State of the World's Plants and Fungi reports (plant diversity and extinction risk): https://www.kew.org/science/state-of-the-worlds-plants-and-fungi
• Field, C. B. et al. (1998), "Primary production of the biosphere", Science 281: 237-240 (global NPP estimates).
• USDA PLANTS Database (identification, native status and distribution): https://plants.usda.gov
• SciOly Wiki, Botany (a cross-check, not a source): https://scioly.org/wiki/index.php/Botany
• Practice more: the Scio.ly test archive has hundreds of public Botany tests.

Condensed facts