Listed below are terms used in the Tree ID Key.
- Achene: Small, dry indehiscent fruit with a single seed.
- Acorn: Fruit composed of a single seeded indehiscent fruit (nut) and its basal cup.
- Alternate: Arranged singly at different heights and on different sides of the stem (nodes).
- Awl-Shaped: Short, narrowly triangular and sharply pointed leaf.
- Axil: Point of the upper angle one plant part makes where it joins another, usually a leaf.
- Basal Sheath: Structure which surrounds the leaves at the base of a cluster.
- Berry: A fleshy one-to-many seeded fruit lacking a pit or core, as the tomato.
- Bract: A much reduced leaf or leaflike structure at the base of a flower. One of the main structures arising from the cone axis in conifers.
- Bristle: Short, stiff hair of hairlike structure.
- Broadleaf: Plant with leaves having a broad blade, like an oak or maple.
- Compound leaf: Leaf composed of two or more leaflets.
- Deciduous: Shedding all or nearly all the foliage each year, not evergreen.
- Drupe: A stone fruit usually one seeded, seed enclosed in stony endocarp inside fleshy outer layer, as in a peach or a cherry.
- Endocarp: Innermost layer that surrounds a seed in a fruit. It may be membranous, like in an apple, or woody, as in a peach.
- Entire: Leaf margin which is not toothed, notched or divided.
- Evergreen: Having foliage that remains green and functional for more than one growing season or at least through the winter or dormant period.
- Glabrous: Without hairs of any kind, not pubescent, smooth.
- Indehiscent: A fruit that does not open at maturity along lines or from a pore.
- Lobe: Rounded division or segment of an organ.
- Lobed: Bearing lobes which are cut less than half way to the base of midvein of the leaf.
- Needle: Slender, needle-shaped leaf, as in a pine needle.
- Node: The place on a stem where at a single level one or more leaves or branches arise.
- Nut: A hard, dry indehiscent fruit, usually with a single seed.
- Opposite: Arranged two at a node on opposite sides of the stem.
- Palmate: Lobed veined or divided from a common point.
- Palmately compound: Compound leaf where three or more leaflets arise from a common point at the end of the petiole.
- Petiole: Stalk or stem of a leaf.
- Pinnately compound: Compound leaf where one of more pairs of leaflets arise from the opposite sides of the elongated axis of the leaf.
- Pubescent: Bearing hairs of any kind, hairy.
- Scale-Like: Thin, flattened leaf, not a broadleaf.
- Simple: Undivided, as in a leaf blade which is not separated into leaflets, although it may be deeply lobed.
- Stalk: Supporting structure of a cone, usually narrower than the cone.
