The keys to identifying elms are height, leaf size and texture, bark and overall shape. All elms are deciduous or semi-deciduous trees with alternate, asymmetrical, toothed leaves that are uneven at the base. Native elms include the American, rock and slippery elms. The Chinese elm is a common imported species.
American elms grow up to 115 feet tall and have rounded or vase-shaped crowns. Their leaves are 4 to 6 inches long and are smooth underneath. Their bark is irregular and scaly.
Rock elms have a maximum height of 80 feet and have cylindrical canopies. Their leaves are 2 to 4 inches long and are hairy on their undersides. Rock elms have corky ridges on their branches.
Slippery elms can grow up to 132 feet in height but are more commonly 40 to 60 feet at maturity. Their canopies are high, umbrella-shaped and less symmetrical than those of American elms. Their leaves are up to 8 inches long and are rough on both sides. Herbal healers have used the mucilaginous inner bark of slippery elm to treat sore throats and dress wounds.
Chinese elms, unlike native species, resist Dutch elm disease. Chinese elms grow up to 70 feet at maturity and have a broad vase shape. Their leaves are up to 2 1/2 inches long and their smooth bark is mottled green, brown, gray and orange with orange or reddish-brown inner bark.