- Tannin Bearing Glands. Tannin producing glands found in various parts of the plant, presumably protective in some structures
- Tap. Persistent, well-developed primary root
- Tendril. Long, slender, coiling branch, adapted for climbing (most tendrils are leaf structures)
- Tentacular. Glandular-haired or tentacle-bearing insectivorous leaf, as in Drosera
- Tepal. A member or segment of perianth in which the parts are not differentiated into distinct sepals and petals
- Terete. Cylindrical and elongate
- Tergeminate. With three orders of leaflets, each bifoliolate, or with geminate leaflets ternately compound
- Terminal. At apex or end of stem. Terminal Bud Scale Scar Rings - Several marks in a ring indicating former places of attachment of bud scales
- Ternately Compound. With leaflets in three's
- Tessellated. Color arranged in small squares, so as to have some resemblance to a checkered pavement
- Testa. The outer, commonly hard and brittle seed-coat
- Tetracyclic. Four-whorled
- Tetrad. Pollen grains in clusters of four
- Tetradynamous. With stamens in two groups, usually four long and two short
- Tetragonal. Four-angled
- Tetrahedral. Having the form of a tetrahedron
- Tetralocular. Four-locular
- Tetramerous. Whorl with four members
- Tetrandrous. With four stamens
- Tetrastichous. Leaves or other structures in four rows
- Theca. One half of anther containing two pollen sacs or male sporangia
- Thorn. A sharp-pointed branch
- Throat. An open, expanded tube in the perianth
- Thyrse. A many-flowered inflorencence with an indeterminate central axis and with many opposite lateral dichasia
- Tiller. A grass shoot produced from the base of the stem
- Tomentose. Covered with dense, interwoven trichomes
- Torose. Cylindrical with contractions at intervals
- Tortuous. Irregularly twisted
- Trailing. Sprawling on ground, usually with adventitious roots
- Transverse or Explanate. At rightangles to long axis
- Tree. A tall, woody perennial plant usually with a single trunk
- Triangular. With three sides and three angles
- Tricarpellate. Three-carpellate
- Trichome. A leaf or stem surface hair
- Tricyclic. Three-whorled
- Tridynamous. With stamens in two equal groups of three
- Trifid. Cut or divided into three lobes or parts
- Triflorous. Three-flowered
- Trifoliate. Three-leaved
- Trifoliolate. With three leaflets
- Trifurcate. Divided into three forks or branches; three-forked
- Trigonous. Three-angled
- Triheteranthous. Having different states in three different sets of flowers, only one state present in each set
- Triheterophytous. Having different states in three different sets of plants, only one state present in each set
- Trilete Spore. Basically tetrahedral, but often appearing round or triangular, with three scar lines forming a Y
- Trimerous. Whorl with three members
- Trimorphic. Having three different shapes and/or sizes within the same species
- Trioecious. Plants staminate, pistillate or perfect
- Tripalmately Compound. With three orders of leaflets, each palmately compound
- Tripinnately Compound. With three orders of leaflets, each pinnately compound
- Triquetrous. Three-angled with the sides usually concave
- Tristichous. Leaves or other structures in three rows
- Triternate. With three orders of leaflets, each ternately compound
- Trullate. With widest axis below middle and with straight margins; ovate but margins straight and angled below middle, trowel-shaped
- Truncate. Cut straight across; ending abruptly almost at right angles to midrib or midvein
- Tryma (Involucre). Two-four loculed nut surrounded by a dehiscent involucre at maturity, as in most species of Carya
- Tube. Cylindrical part
- Tuber. A thick storage stem, usually not upright
- Tuberculate. With hard, swollen, persistent base or tubercle. Tuberculate or Verrucose - With a warty surface
- Tubercules. Silica deposits on the stem ridges, as in Equisetum
- Tuberous. Fleshy roots resembling stem tubers
- Tubular. Cylindrical
- Turbinate. Top-shaped; obconic
- Turgid. Tumid or swollen
- Turion. An over-wintering bud, as in Lemna
- Twining. Twisted around a central axis
- Umbel. A determinate or indeterminate flat-topped or convex inflorescence with the pedicels arising at a common point. Compound Umbel - An umbel with primary rays or peduncles arising at a common point with a secondary umbel arising from the tip of the primary rays; a branched umbel
- Umbellet. The secondary umbel in a compound umbel
- Umbilicate. Depressed in the center
- Umbo. Projection, with or without spine or prickle, on the apophysis of the cone scale
- Umbonate. Round with a projection in center
- Umbraculate. Umbrella-shaped, as in Sarracenia
- Umbraculiform. Umbrella-shaped
- Undulate. With a series of vertical curves at right angles to the central axis
- Unguiculate. Clawed
- Unicarpellous or Stylodious. With solitary, free carpel in gynoecium
- Unifoliolate. With a single leaflet with a petiolule distinct from the petiole of the whole leaf, as in Cercis
- Unilocular. One-locular
- Uninodal Shoot. Spring shoot developing from the terminal winter bud and producing only one internode with one whorl of branches at the end; the cones are subterminal at the end of the shoot; e.g., Pinus resinosa
- Uniseriate. One-rowed; in one series
- Unisexual. With only one sex in each flower
- Urceolate. Urn-shaped
- Stinging Urent. With erect, usually long trichomes that produce irritation when touched
- Utricle. A small, bladdery or inflated, one-seeded, dry fruit.
- Vallecular Canal. A canal beneath a stem groove
- Valvate. Sides enrolled, adaxially or abaxially so that margins touch
- Valvular. Dehiscing through a pore covered by a flap of tissue. Valvular or Septifragal Capsule - One with valves breaking away from the septa, as in Ipomoea
- Variegated. The color disposed in various irregular, sinuous, spaces
- Bundle or Trace Scar. Vascular Bundle or Trace Scar A mark indicating former place of attachment within the leaf scar of the vascular bundle or trace
- Vegetative Frond. Frond lacking sporangia
- Velum. The membranous flap covering the sporangium, as in Isoetes
- Velutinous. Covered with dense, straight, long and soft trichomes; pile-like
- Ventral. Pertaining to the surface nearest the axis; inner face of an organ; the upper surface of the leaf; adaxial. Ventral Side - Top side or upper side of a perianth part
- Ventricose. Inflated on one side near the middle
- Ventristipular. On ventral side of stipule
- Vermiform. Worm-shaped
- Vernal. Appearing in spring
- Verrucose. Warty
- Versatile. Dorsifixed but anther seemingly swinging free on the filament
- Verticillaster. Whorled dichasia at the nodes of an elongate rachis
- Vespertine. With flowers opening in the evening or night; appearing or expanding in the evening
- Vestigial. Minute; a remnant
- Vexillate. Having one structure larger than others which is folded over smaller enclosed structures
- Villosulous. Minutely villous
- Villous. Covered with long, soft, crooked trichomes
- Vine or Liana. An elongate, weak-stemmed, often climbing annual or perennial plant, with herbaceous or woody texture
- Virgate. Wand-like; long, slender, and straight
- Viscid. Sticky or glutinous
- Whorl. A cyclic or acyclic group of sepals, or petals, or stamens, or carpels
- Whorled, Radiate, or Verticillate. Three or more leaves or other structures per node
- Wing. Lateral petals, as in the Fabaceae; a flattened extension, appendage or projection from a perianth part
- Winged. With flattened blade-like margins. Winged Nut (Bract) - Nut enclosed in a winglike bract, as in Carpinus
- Wood. Xylem consisting of vessels and/or tracheids, fibers, and parenchyma cells
- Woody. Hard and lignified
- Zoned. The same as ocellated, but the concentric bands more numerous
- Zonocaulous. With branches intermittently spaced along main stem
- Zygomorphic or Bilateral. With floral parts in two symmetrical halves