A minority of trees have compound leaves, i.e., multiple leaflets on a single leaf stem, giving many species a feathery beauty and the student means of identification.
Compound leaves can be either pinnate, or feather-compound, with leaflets lining the two sides of the stem, or, less commonly, palmate, or fan-compound, with leaflets emerging from the end of the stem like the spokes of a wheel. Except for horsechestnut and buckeye, the common compound-leaved trees have pinnate leaves.
Because the multiple leaflets are heavy, most of these trees have fairly stout twigs and large leaf scars, the bases of the leaves being extra thick to support the connection with the twig.
- Opposite trees with compound leaves:
Horsechestnut: Palmate leaves, opposite buds (but the heavy leaves frequently break off, making the pattern appear to be alternate). Sticky buds; showy white flowers in large upright clusters; hard, shiny nuts in fall. This is a non-native species that has escaped cultivation in the East.
Buckeye: Related to horsechestnut, several species of the native buckeye grow west of the Appalachians, also with palmate leaves, nuts, and showy flowers, usually yellow. Both horsechestnut and buckeye are somewhat toxic, although the bark and seeds are used medicinally for circulatory problems such as varicose veins, hemorrhoids, and glaucoma, according to herbalist Matthew Wood.
Ash: Opposite leaves with 5-9 egg-shaped leaflets, depending on species, sometimes toothed and sometimes not. The terminal leaflet (the one at the end of the leaf stem) is about the same size as the side leaflets. Each seed is contained within a single flat membrane, similar to the double, winged “keys” of the maple (another tree with opposite leaves).
Box Elder/Ashleaf Maple: Intermediate between ash and maple, box elder has opposite, coarsely toothed leaves with 3-5 leaflets and the double, winged “keys” of the maple. Young leaves often have three leaflets and resemble poison ivy. Twigs have a bluish tinge and a powdery “blush” that rubs off.
- Alternate trees with compound leaves:
Sumac: A shrub or small tree with 7-31 narrow, pointed leaflets. Poison sumac has white berries and grows only in swamps. Staghorn sumac and other non-poisonous species have spires of red berries that ripen in late summer and persist throughout the winter.
Black Walnut: Pinnate leaves with 7-17 narrow, pointed leaflets. The end leaflet is often absent. Crushed leaves have a spicy scent. Nuts occur in thick, spherical, one-piece husks.
Butternut: Similar to black walnut, except that twigs are downy, and nuts are oblong, with sticky husks.
Ailanthus: Pinnate leaves with 11-41 leaflets having a small lobe near each leaf base that contains a tiny round gland. Crushed leaves smell like peanut butter. Male flowers occur in large, yellowish clusters that have an unpleasant odor. A fast-growing tree, common in cities.
Hickory: Most species have the end leaflet larger than the side leaflets and long points at the ends of the leaflets. Nuts have husks that split into four parts upon ripening, some species splitting all the way to the base.
Honey Locust: Many small, narrow leaflets; thorns over one inch long protruding from the dark bark; long, twisting seed pods with smooth, bean-like seeds within.
Black Locust: Smallish, egg-shaped leaflets; thorns paired, under one inch long, occurring at leaf scars; thick, flat seed pods.
For information on identifying trees with non-compound leaves, see Trees with Simple Leaves.
