American elm is a small to medium-sized (to very large) tree, at maturity with spreading branches forming a broad-spreading, fan-shaped crown.
Leaves are alternate, simple, 4–6 inches long, 2–3 inches wide, broadest at or below the middle with coarse, sawtooth edges. Smaller teeth appear along the lower side of the larger teeth. Base is uneven. Upper surface dark green, shiny, mostly smooth to somewhat rough.
Bark is gray, in cross-section with alternating brown and white layers, grooves deep, ridges flattened with thin closely pressed scales.
Twigs are slender, reddish-brown turning ash gray with age, hairy at first, smooth later.
Flowers February–April, in drooping clusters, red to green, small, petals lacking, the flower stalks originating from the same point.
Fruits March–May, in drooping clusters on long stalks originating from the same point; fruit about ½ inch long, seed surrounded by a thin wing; wing broadest in the middle, notched at the tip, with a fringe of silvery hairs along the edge.
Height: to 70 feet or more, but trees that large are rare today; most are smaller, understory trees.
Habitat and Conservation
Although essentially a bottomland tree, American elm will grow under a variety of conditions. Sadly, a fungus was imported to North America on logs shipped from Europe around 1930. This “Dutch elm” fungus spread quickly and began killing thousands of large, magnificent trees. The fungus is transmitted by elm bark beetles that chew on one tree and then fly to another. The fungus enters the sapwood and blocks the flow of water into the tree, causing branches to wilt and die, killing the tree before it can reach a large size.
Populations are secure, but Dutch elm disease, introduced from Europe in 1941, killed off nearly all the majestic old elms that had once been a fixture in nearly every town. The species survives because even young trees can produce viable seed. However, as new trees grow, they eventually succumb to the disease and die before they get very big. Disease-resistant strains are being developed, and individual trees can be treated with fungicide injections every three years.
With their arching branches, American elms were the shade tree of choice for town squares and city streets, and they have figured into many historic American events. Elms can live for hundreds of years, so it has been traumatic for Americans to lose trees that were essentially historical markers. When all the large street elms died, people planted ash trees as an alternative, but now ashes are endangered continent-wide because of the invasive, exotic emerald ash borer. When the ashes are gone, what will be America's next popular shade tree?
Elms are prolific producers of seeds, and birds, rabbits, opossums, squirrels, and rodents eat them. Deer eat the leaves and twigs in the spring.