Botany Terms Starting With T
Botany Glossary: T
Taproot
/ TAP-root / · Old English taeppan (to tap) + rot (root)
Taproot is a primary root that develops directly from the radicle of a seedling, grows vertically downward, and gives rise to smaller lateral roots, often serving as the plant's main organ for water absorption and carbohydrate storage.
Taproots typically penetrate 1 to 3 meters into the soil, reaching moisture layers inaccessible to shallow fibrous root systems. In desert-adapted mesquite trees (Prosopis juliflora), taproots have been documented at depths exceeding 50 meters, allowing the tree to access permanent groundwater in arid environments. Cultivated plants such as carrots (Daucus carota) and sugar beets (Beta vulgaris) have been selectively bred for enlarged, starch- or sugar-rich taproots; sugar beet roots can accumulate sucrose at concentrations reaching 15 to 20 percent of fresh mass.
Lateral roots branch from the taproot at intervals, absorbing water and minerals from the surrounding soil volume while the taproot itself anchors the plant against uprooting forces.
Oak trees (Quercus spp.) develop a deep taproot during their first few years of growth that can descend more than 1.5 meters before the tree reaches knee height above ground. This early investment in a deep anchor root is one reason oaks are notoriously difficult to transplant successfully once they are more than a year or two old.
Desert Flowers →All plants develop a taproot from their primary root. Monocots, including all grasses and most cereal crops, lack a persistent taproot entirely; their radicle degenerates shortly after germination and is replaced by a fibrous system of adventitious roots arising from the stem base.
Carrots and Parsleys Flowers →In dandelions (Taraxacum officinale), the taproot can extend 30 centimeters or more below the soil surface and stores enough carbohydrate reserves to regenerate a full rosette of leaves if the shoot is removed. Because the taproot's regenerative crown sits several centimeters below the surface, mowing or hand-pulling that leaves even a short root fragment allows the plant to regrow within days.
Tendril
/ TEN-dril / · Old French tendrillon (young shoot)
Tendril is a slender, elongated plant organ derived from a modified leaf, stem, stipule, or flower stalk that coils around a support structure through a touch-sensitive growth response, anchoring climbing plants to their substrate.
Contact with a support triggers a thigmotropic response in which cells on the side of the tendril touching the object grow more slowly than cells on the opposite side, causing the tendril to curl around the support within minutes to hours. In common grapevine (Vitis vinifera), tendrils are modified stem branches that can exert gripping forces approaching 1 newton and, once anchored, develop a helical coil along their length that forms a spring, absorbing wind-load forces that would otherwise tear the attachment point free. Garden peas (Pisum sativum) produce tendrils from modified leaflets at the tips of compound leaves, allowing the plant to climb a 2-meter support structure without producing any woody tissue.
Some species in the genus Passiflora develop adhesive pads at tendril tips that bond to rough surfaces with forces exceeding the tensile strength of the tendril itself.
Virginia creeper (Parthenocissus quinquefolia) produces tendrils tipped with adhesive discs that secrete a glue-like compound when pressed against a surface, generating attachment forces strong enough to support the vine on smooth glass or painted walls. Chemical analysis of the adhesive has identified a mixture of polysaccharides and proteins that harden on contact with air, making Virginia creeper one of the few plants studied for bio-inspired adhesive materials.
Tendrils are always modified leaves. Tendrils arise from different organs depending on the species: stems in grapevines, leaflets in peas, stipules in greenbrier Smilax spp., and flower stalks in passionflowers.
In sweet pea (Lathyrus odoratus), the terminal leaflets of each compound leaf are modified into tendrils that begin coiling within 20 to 30 minutes of contacting a support. A single tendril can complete one full spiral turn around a 3-millimeter wire within about 2 hours, and a climbing plant typically produces new tendrils every few days during active growth.
Terpene
/ TER-peen / · Terpentin (German for turpentine) + -ene, chemical suffix
Terpene is any member of a large class of hydrocarbons synthesized by plants and other organisms from repeating five-carbon isoprene units, encompassing compounds that range from volatile aromatic molecules to structural pigments and hormones.
Plants assemble terpenes through two biosynthetic pathways: the mevalonate pathway in the cytoplasm and the methylerythritol phosphate pathway in plastids, both of which produce the five-carbon precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate. Monoterpenes, built from two isoprene units, include limonene in citrus peel and linalool in lavender (Lavandula angustifolia), and these volatile compounds evaporate readily at ambient temperatures to produce the characteristic scents that attract pollinators or repel herbivores. Diterpenes, assembled from four isoprene units, include the resin acids that conifers such as ponderosa pine (Pinus ponderosa) secrete into resin ducts to entrap and chemically deter bark beetles.
Tetraterpenes, built from eight isoprene units, include the carotenoid pigments that color ripe tomatoes and carrot roots and that protect photosynthetic membranes from excess light energy.
Taxol (paclitaxel), a diterpene first isolated from the bark of Pacific yew (Taxus brevifolia) in 1971 by Monroe Wall and Mansukh Wani, became one of the most widely used chemotherapy drugs in the world. Harvesting enough taxol from wild yew bark to treat a single cancer patient originally required stripping the bark from several mature trees, driving the development of semi-synthetic production routes from yew needles.
Terpenes are only fragrant compounds responsible for plant scents. Terpenes also include non-volatile compounds such as carotenoid pigments, the plant hormone gibberellin, the rubber polymer of Hevea brasiliensis, and the sterol precursors of cell membranes, none of which have any role in scent production.
Ponderosa pine (Pinus ponderosa) produces a mixture of monoterpenes and diterpene resin acids in its resin ducts, releasing up to several grams of volatile terpenes per tree per day during warm weather. When bark beetles attack, the tree increases resin flow within hours, and the terpene mixture both physically engulfs the beetles and delivers toxic compounds that can kill or repel an infestation before it establishes.
Thigmonasty
/ THIG-moh-NAS-tee / · Scientific term used in plant movement.
Thigmonasty is a plant movement triggered by touch or vibration, independent of the direction of the stimulus.
Thigmonasty occurs through rapid turgor changes in specialized cells called pulvini, located at the base of leaves or leaflets. When touched, ion channels in pulvinar cells open and potassium ions flood out, causing water to leave by osmosis and internal pressure to drop within seconds. The leaf or leaflet then collapses or folds without any net cell growth, distinguishing thigmonasty from directional growth responses such as thigmotropism.
Sensitive plant (Mimosa pudica) leaflets complete this folding movement in under one second and can repeat it multiple times without permanent structural change.
The Venus flytrap (Dionaea muscipula) snaps shut only after two trigger hairs are touched within about 20 seconds of each other, a counting mechanism that prevents the plant from wasting energy on false alarms like falling raindrops.
Thigmotropism →Thigmonasty is growth toward touch. Thigmonasty involves no cell growth at all; it is a reversible turgor-driven movement that can repeat many times in the same tissue.
Sundew plants (Drosera rotundifolia) show thigmonastic leaf curling when an insect contacts their sticky tentacles, folding the leaf around prey within 10 to 30 minutes through turgor pressure changes rather than growth. The tentacles curl inward within 10 to 35 seconds of contact, driven by differential turgor changes in motor cells at the tentacle base rather than by growth, and they return to the extended position within 10 to 30 minutes if no prey is captured. In Drosera capensis, repeated stimulation with a glass rod elicits progressively slower recovery times, demonstrating a form of habituation that distinguishes thigmonasty from purely mechanical bending.
Transpiration
/ trans-pih-RAY-shun / · Latin trans (across) + spirare (to breathe)
Transpiration is the process by which water absorbed by plant roots moves through the plant body and exits as water vapor, primarily through stomatal pores on leaf surfaces.
A single maize plant can release roughly 200 liters of water during a growing season, with 90 percent or more of all absorbed water lost this way. Stomata, the microscopic pores on leaves, remain open during the day to admit carbon dioxide for photosynthesis, simultaneously allowing water vapor to escape. This water loss creates negative pressure in xylem vessels that pulls water columns upward from roots, a mechanism sufficient to lift water more than 100 meters in tall coast redwoods (Sequoia sempervirens).
Leaf temperature can drop by 10 degrees Celsius or more through the evaporative cooling that accompanies this water loss.
Desert plants called resurrection plants, such as rose of Jericho (Anastatica hierochuntica), can lose nearly all their water and survive complete desiccation, then rehydrate and resume transpiration within hours of rainfall, a tolerance no typical crop plant possesses.
Transpiration is wasteful water loss with no benefit to the plant. Transpiration drives the upward movement of dissolved minerals from roots to leaves and cools leaf tissue during intense sunlight.
In a tomato plant (Solanum lycopersicum), transpiration peaks at midday when stomata are fully open for photosynthesis. A single sunflower (Helianthus annuus) leaf can lose approximately 1 gram of water per hour on a hot, dry day.
Trichome
/ TRY-kohm / · Greek trichoma (hair growth)
Trichome is a hair-like epidermal outgrowth on the surface of a plant that may protect against herbivores, reduce water loss, or secrete chemical compounds.
Trichomes vary considerably in structure, ranging from glandular types that secrete compounds to stinging types and reflective types that reduce light absorption in bright environments. Stinging nettle (Urtica dioica) possesses hollow trichomes tipped with silica that break upon contact and inject a mixture of formic acid, histamine, and acetylcholine into skin. In cannabis (Cannabis sativa), glandular trichomes concentrate cannabinoids and terpenes within their secretory heads.
Tomato (Solanum lycopersicum) plants carry at least six morphologically distinct trichome types, some of which trap and kill small insects with sticky exudates while others release volatile compounds that repel larger herbivores.
Some carnivorous plants, including sundews (Drosera spp.), bear glandular trichomes called tentacles that secrete both adhesive mucilage to trap insects and digestive enzymes to break down captured prey, making the same structure responsible for capture and digestion.
Trichomes are simple surface hairs with no biological function. Trichomes are among the most functionally diverse epidermal structures in plants, with documented roles in herbivore deterrence, pathogen resistance, UV protection, and chemical secretion.
Current Environmental Issues in the US →Mint leaves (Mentha spicata) carry glandular trichomes packed with menthol and other volatile oils. Each trichome head ruptures easily when the leaf is touched, releasing the characteristic scent that deters many leaf-feeding insects.
Woody Aromatic Flowers →Trimerous
/ TRY-mer-us / · Scientific term used in flower structure.
Trimerous is a term describing flowers whose sepals, petals, and stamens are arranged in whorls of three or multiples of three.
Trimerous flowers contain floral organs in multiples of three, such as three sepals and three petals per whorl, or six petals arranged in two whorls of three. This pattern appears in approximately 65 percent of monocot species, including lilies (Lilium spp.), daffodils (Narcissus spp.), and tulips (Tulipa spp.). The three-part symmetry contrasts with the four- or five-part symmetry typical of eudicots and gives botanists a reliable character for distinguishing monocots from dicots during field identification.
Genetic control of floral organ number involves the ABC model genes, which specify the identity of petals, stamens, and carpels in predictable, repeating arrangements.
Orchids (family Orchidaceae) are trimerous, yet their three petals are so unequal in size and shape that the three-part plan is nearly invisible to casual observers; one petal is dramatically enlarged into the lip, or labellum, that guides pollinators toward the reproductive structures.
Trimerous means a flower has exactly three petals. Trimerous describes a pattern in which all floral whorls, including sepals, petals, and stamens, occur in threes or multiples of three, not petals alone.
Iris flowers (Iris germanica) display a trimerous structure with three drooping outer tepals alternating with three upright inner tepals, plus three stamens and a three-chambered ovary. Each of the three style branches is petal-like and arches over a single stamen, a configuration that forces visiting bees to contact both anther and stigma.
Turgor Pressure
/ TUR-ger PRESH-er / · Latin turgere (to swell) + pressura (pressing)
Turgor pressure is the outward force that water exerts against a plant cell wall after entering the cell by osmosis, keeping soft plant tissues firm and upright.
Plant cell turgor pressure typically ranges from 0.5 to 5 megapascals in healthy herbaceous plants, with values reaching 10 megapascals in some specialized cells. When the central vacuole fills with water, the expanding membrane presses against the rigid cell wall, keeping the cell inflated much like a pressurized balloon. In celery stalks, turgor pressure in epidermal and cortical cells maintains crispness; losing just 10 percent of cellular water causes noticeable wilting.
Guard cells surrounding stomata exploit this mechanism directly, swelling to open stomatal pores when water enters and shrinking to close them when water leaves.
The squirting cucumber (Ecballium elaterium) builds turgor pressure inside its fruit to more than 27 times atmospheric pressure, then explosively ejects seeds up to 10 meters when the fruit detaches from its stalk.
Central Vacuole →Turgor pressure comes from air trapped inside plant cells. Turgor pressure results entirely from water drawn into the vacuole by osmosis, which then pushes outward against the cell wall.
Discover Cell Wall Functions →In lettuce leaves, turgor pressure keeps cells rigid and prevents wilting. When placed in a concentrated salt solution, lettuce loses turgor pressure and becomes limp within minutes as water moves out of cells by osmosis.