At first glance, ash and elm trees may look quite similar. Both ash trees and elms produce winged seeds, or "fruits." Ashes and elms are very different upon closer inspection, however, and are even rather different among their individual species. Distinguishing between ash and elm trees isn't difficult, if you know what to look for. You'll have to look even closer, however, when you want to identify the exact ash or elm tree species.
Identify Ash Trees
Identify the white ash tree (Fraxinus Americana) by its compound, oppositely-arranged leaves with toothed edges and uniformed leaflets. The white ash reaches 60 to 80 feet tall at maturity with a 2 to 4 foot trunk diameter. The gray bark has diamond-shaped furrows and intertwined ridges. The white ash bears single-winged, elongated "fruits" holding their seeds that are 1/4-inch wide and tapered.
Look for a 30- to 60-foot-tall ash tree with a 1 to 3 foot trunk diameter to spot the green (or red) ash (F. pennsylvanica). The green ash has the same types of leaves and fruits as the white ash, but its fruits are strongly tapered and even narrower, only 1/8-inch wide. Also, the green ash has hairy twigs and leaf stalks, while the white ash has smooth ones. Like the white ash, the green ash has firm, ridged bark.
Identify the blue ash (F. quadrangulata) by its gray, shaggy and scaly plated bark. The blue ash reaches about 40 to 60 feet in height with a 1 to 2 foot trunk diameter and has compound leaves that can be 8 to 12 inches long. The oppositely-arranged leaves have leaflets that are toothed and have short stems. The blue ash's fruits are single-winged and elongated like other ash trees, but they're wider and more oblong.
Look for an ash tree that's similar in height and trunk diameter as the blue ash, but has compound, opposite, toothed leaves that have leaflets without stems to spot the black ash (F. nigra). The black ash also has similar-shaped fruits as the blue ash, but the bark on the black ash is soft, gray and divided into scaly plates, which are easily rubbed off into a powder.
Identify Elm Trees
Identify the elm tree by its height. The Scotch elm, Siberian elm, English elm and slippery elm are the tallest of elm trees, growing up to 132 feet. The American elm reaches a height of 115 feet, while the rock elm grows to 80 feet tall. The Chinese elm grows 20 to 60 feet at maturity and the winged elm reaches a mature height of 40 to 50 feet. The camperdown elm is the smallest, growing to only 10 or 15 feet in height.
Identify elms by the size of their leaves. All elm tree leaves are simple, broad, flat, not lobed and have fine, double-toothed edges. The Siberian and winged elms have the smallest leaves, only 1 to 3 inches long, and the Chinese elm's leaves are 4/5- to 2 and 1/2-inches long. The slippery elm's leaves are the largest, up to eight inches long, and the camperdown elm has leaves that are up to seven inches long. The rock elm has 2- to 4-inch-long leaves, the scotch and English elms have 3- to 6-inch-long leaves and the American elm has 4- to 6-inch-long leaves.
Study the bark to identify elms. The Chinese elm has smooth, mottled brown bark that sheds in thin flakes to reveal orange or reddish-brown inner bark. The winged elm's bark has flat scaly ridges with irregular, shallow furrows in between, while the Siberian elm has gray, rough bark. The rock elm has corky ridges on its branches and the American elm has irregular scaly bark.
Identify elm trees by their shape or form. The American and Scotch elms have rounded canopies, with the American elm often forming more of a vase-shaped crown. The rock elm has a cylindrical shape to its canopy. The slippery elm has an umbrella-shaped, high canopy, the camperdown elm has an umbrella-like, weeping form with drooping branches, the Siberian elm has a very wide, oblong canopy, the English elm has a slightly narrow but rounded crown, and the Chinese elm has a broad, vase-like shape to its canopy.
Study the leaf texture to identify elm trees. The slippery elm's leaves are very rough on both sides, while the Chinese and American elm's leaves aren't rough underneath. The rock elm's leaves are hairy on the undersides, while the English elm has leaves with rough top surfaces and hairy undersides.