Identifying Features of Trees
Terms to know when studying tree identification
When learning to identify trees, it helps to know the features by which trees are grouped, and the terms that are used to describe them in literature and field guides.
Most trees have simple leaves, with one leaflet per stem, as in maple, oak, birch, beech, and many other species. Leaves may be toothed, with blunt or jagged teeth; lobed, with curved or pointed areas protruding; or entire, smooth-edged without teeth or lobes.
A substantial number of trees have compound leaves, composed of multiple leaflets borne by a long leaf stem which falls off in the fall, or sometimes later in winter. Examples are ash, walnut, butternut, hickory, all of which are pinnate (sometimes called feather-compound), meaning that the leaflets line both sides of the stem, like the shafts of a feather. A few compound leaves, such as horse chestnut, are palmate, with the leaflets arising fanwise from the tip of the stem, like fingers on the palm of the hand. Compound leaves are usually heavy and require thick twigs for support. An exception is black locust, whose oval leaflets are quite small and are borne on relatively thin twigs.
Leaves may be arranged in opposite or alternate patterns on the twigs. See the article "Opposite Tree Identification" for details.
When a leaf withers and falls in autumn, a leaf scar is left behind where the leaf stem breaks from the twig. Usually lighter in color than the bark, the scar is marked with tiny dots from the breakage of the vessels carrying water and nourishment to and from the leaves. Each species has a specific number of these vessels, which occur in bundles, and the scars they leave behind are called bundle scars. The size and shape of the leaf scar reflects the size and shape of the leaf stem, which may be curved or lobed to support the weight of a compound or large simple leaf while maximizing surface area. Large leaves also have large numbers of bundle scars, while a small leaf might have only two or three.
Each species has distinctive buds, which form in summer when the tree is growing and remain on the twigs throughout the fall and winter, providing clues to the tree’s identity. Buds are located at the growing tip of the twig and just above each leaf or leaf scar. Sumac buds are unusual in that they form inside the circular leaf stem.
The size of the bud often corresponds to the size of the leaf. Buds are enclosed in tough, waxy bud scales, whose number and arrangement depend on the species. Some species, such as maple and oak, have a number of imbricate scales, overlapping like shingles on a roof. Willow buds have a single scale, while basswood has two. Horse chestnut has large, sticky buds. Balsam poplar buds are fragrant. Though largely overlooked, buds can provide a fascinating way to study trees in winter. For tips on studying trees, see "Learning to Identify Trees".
