By Dr. Leonard Perry, Extension Professor
University of Vermont
As with any language, knowing the terms and words helps you understand what is being said. Learning the "language of leaves" will help you understand what serious gardeners are talking about or what you may read in book and catalog descriptions.
To understand leaves, you should have a passing knowledge of the blades and how they are attached to stems and the leaf (its shape, margins, divisions, and surfaces).
Leaf blades can be opposite each other on the stem--"alternate" (not opposite), or "whorled" (from a single point). If they don't come from the stem, but from the base of the plant, they are "basal." They may be attached to the stem with short stems called "petioles." If directly attached to stems with no petioles, they are "sessile." You can check out other terms for the bases of leaves and tips in garden encyclopedias or even on the Internet under glossaries of botanical terms.
Leaf shape is probably the most noticeable and important trait for gardeners, and there are many shapes and terms. The main terms you may see include "linear"--narrow, the same width throughout; "oblong"--two to three times as long as wide with parallel sides; or "elliptic"--broadest in the middle with tapering ends like a football.
If broadest below the middle, toward the leaf base or part attached to the stem, the leaf is lance-shaped or "lanceolate." If just the opposite, then "oblanceolate." The same applies to egg-shaped or "ovate," and "obovate." The meaning of other terms are easy to guess--"orbicular" meaning circular, "spatulate" as in spoon-shaped (like a kitchen spatula), and "reniform" or kidney-shaped.
Margins or edges of leaves can be smooth, curved downward, or rolled inward--"revolute," wavy or "sinuate," hairy or "ciliate," or toothed with various indentations. If these "teeth" on leaf margins are broad and rounded, the leaf is "crenate;" pointed outward as steps--"dentate;" sharply cut--"serrate;" and deeply cut and irregular--"incised."
Many garden flowers have entire leaves with no divisions. But if divided, they are called "compound." Divisions that branch off, like with spider flower (Cleome), Astilbe, or marigold, are called "pinnate." Leaf divisions arising from the same point, or "palmate," are less common in garden flowers.
Finally, you need to know about the leaf surfaces--"glabrous" or smooth, "glaucous" or waxy (often white or blue color), and hairy. Hairy leaves are sometimes referred to in other terms, depending on length and types of hairs. It's enough for most gardeners just to recognize that terms like "pubescent," "rugose" or "tomentose," refer to hairs on the leaf surfaces. These hairs may help leaves resist droughts or attacks from insects and diseases.
Reread this article, learn these terms, and you'll feel much more comfortable when reading descriptions of garden flowers. You'll be able to read the more advanced books on flowers and not feel lost when talking with garden professionals who use these terms as a matter of speech.
Look at your garden flowers this season and try to find some examples
of each term. This way you'll really make them your own. Practice using
them, as you would new words in any language, and not only will it help
you learn them, but you'll undoubtedly impress your gardening neighbors,