Tetrahedral. Having, or made up of, four faces (triangles).
Thorn. A stiff, woody, sharp-pointed projection.
Tolerant. Capable of enduring more or less heavy shade.
Tomentose. Densely pubescent with matted wool.
Toothed. With teeth or short projections.
Torus. The part of the axis of a flower which bears the floral organs.
Transverse. Said of a wood section made at right angles with the axis of the stem; across the grain.
Tree. Usually defined as a plant with a woody stem, unbranched at or near the base, reaching a height of at least 15 feet.
Trunk. The main stem of a tree.
Turbinate. Top-shaped.