Gardeners often wonder at the immense variety of leaf forms. In fact, this amazing show of diversity is one of the reasons we’re engaged with the pleasures of mixing plants and trees in our landscapes.
“Leaves are engineering marvels,” writes Brian Capon, in his book Botany for Gardeners, an excellent guide to the inside story on the science of plant biology. For example, leaves always grow in an organized pattern along a stem or stalk. Some common ways in which they develop are basal, growing from the base (e.g., tulips); opposite, growing across from each other (e.g., maples); whorled, arranged in a ring around the stem (e.g., Joe Pyeweed); or alternate, staggered along the stem (e.g., pagoda dogwood).
These various growth patterns ensure individual leaves cast as little shade on one another as possible, allowing a maximum amount of light to be absorbed for photosynthesis (the process by which plants capture sunlight and—with the help of water, soil minerals and carbon dioxide—turn it into food. Think of sunbathing as the equivalent of getting breakfast, lunch and dinner served up daily).
Although the first leaves of most seedlings look more or less the same, as they grow, the foliage reveals the unique pattern, shape and size of their species. Some plants have a simple leaf: the blade is a single unit and is not divided into leaflets (e.g., hydrangeas, magnolias), while others grow compound leaves, with two or more leaflets (e.g., walnuts, ash trees). Some leaves, like those of maidenhair fern for example, look feathery because they have compound leaves that are further divided into smaller sections.
Common leaf terms
|Deltoid||Triangle-shaped; eg. grey birch (Betula populifolia)|
|Elliptic||Narrow, oval-shaped and longer than they are wide with symmetrically curved margins (edges). Widest at the middle; eg. chestnuts (Castanea spp.)|
|Lanceolate||Longer than they are wide, shaped like the tip of a lance; eg. willows (Salix spp.)|
Long and narrow (more than 12 times longer than they are wide); eg. most grasses
|Oveate||Egg-shaped (widest below the middle); eg. mock orange (Philadelphus coronarius)|
|Cordate||The entire leaf is heart shaped, from its notched base to its pointed top; eg. eastern redbud (Cercis canadensis)|
|Palmate||Leaves with the leaflets attached to a common point (like human fingers to a hand); e. Japanese maple (Acer palmatum)|
Feather-shaped, with the lobes arranged on either side of a central vein; eg. Christmas fern (Polystichum acrostichoides)
|Pinnately compound||Leaves made up of leaflets arranged along a central stalk; eg. black walnut (Juglans nigra)|
|Trifolate||Having three leaflet; eg. common hoptree (Ptelea trifoliata)|