American Elm
Ulmus americana
Elm family (Ulmaceae)

Description: At maturity, this tree is 60-100' tall, forming a trunk 2-4' across and an arching crown with drooping branchlets. The trunk is long and undivided in forested areas, but it is shorter in open areas before dividing into major branches. On young trees, trunk bark is gray and slightly rough overall, but it often has irregular longitudinal stripes that are colored black and white. On older trees, trunk bark is gray and more furrowed. Branches and branchlets have gray bark that is more smooth, while twigs are smooth, brown, and terete. Alternate deciduous leaves occur along the twigs and branchlets; they are typically arranged in 2 rows. The leaf blades are 3-5" long and 1-3" across; they are ovate to ovate-obovate and doubly serrated along their margins. The upper surface of the blades is medium green and smooth to slightly rough in texture (hairs are not readily visible). The lower surface of the blades is pale green and largely hairless, except for small tufts of white hair in the axils of the major veins. The major veins on the leaf undersides are often short-pubescent or canescent. The petioles are whitish or yellowish green, often short-pubescent or canescent, and very short (less than " in length). The leaf blades are pinnately veined with about 15 pairs of lateral veins. The lateral veins are relatively straight and run parallel to each other. On each side of the central vein, there are 0-3 lateral veins that become conspicuously forked near the leaf margins, otherwise they are undivided.



Toward the tips of last year's branches, perfect flowers develop in small clusters of 3-5. There are several drooping flowers per cluster; their pedicels are about " long. Individual flowers are about 1/8" across, consisting of a short calyx with 7-9 lobes, an ovary with a divided style, and 7-9 stamens. The calyx is typically reddish green, while the anthers are red (but becoming dark-colored with age). These flowers bloom during early to mid-spring for about 1-2 weeks; they are cross-pollinated primarily by the wind. The flowers are replaced by flattened single-seeded samaras about 1/3" (8 mm.) long and a little less across; they are ovate in shape, except for notches at their tips. The samaras have long hairs along their margins (ciliate), otherwise they are hairless. In the center of each samara is an ellipsoid seed that is somewhat flattened; it is surrounded by a membranous wing. At maturity during the late spring or early summer, the samaras usually become light tan (sometimes they are reddish). The samaras are distributed by the wind. In moist areas, the woody root system is shallow and spreading, but in dry areas it is more deep and develops a taproot. During the autumn, leaves turn yellow before falling to the ground.

Cultivation: The preference is full sun to light shade, moist to mesic areas, and fertile loamy soil. However, American Elm will adapt to drier areas and it can tolerate a wide range of soil types, including those that contain clay, silt, or sand. Temporary flooding is tolerated during the winter dormancy period, otherwise good drainage is required. Because of this tree's vulnerability to Dutch Elm Disease, Phloem Necrosis, and other problems, it tends to be short-lived and usually fails to reach its mature size. It can be propagated by leaf bud cuttings.

Range & Habitat: While there has been some population decline because of disease organisms, the native American Elm is still common within Illinois; it has been found in every county (see Distribution Map). Habitats include moist to mesic deciduous woodlands, savannas, woodland openings, woodland borders, wooded terraces along major rivers, flatwoods in upland areas, shaded banks of rivers and streams, higher ground in swamps, fence rows, and roadsides. Today, American Elm is found primarily as an understory tree in both higher quality habitats and disturbed areas. At one time, it was an important canopy tree in deciduous woodlands throughout the state, particularly in bottomland areas. Some older trees are still found in isolated urban areas. Prior to the mid-20th century, American Elm was often used as a landscape tree along streets.

Faunal Associations: Even though the flowers are primarily wind-pollinated, honeybees sometimes collect pollen from them, and they may function as minor pollinators. This is possible because the flowers are perfect, rather than unisexual. Some insects feed on the foliage and other parts of American Elm and other elms (Ulmus spp.); this includes the caterpillars of the butterflies Polygonia comma (Comma) and Polygonia interrogationis (Questionmark). Elms are also host plants for the caterpillars of Nerice bidentata (Double-Toothed Prominent), Ceratomia amyntor (Elm Sphinx), and other moths. Elms are the winter hosts of several Eriosoma spp. (Woolly Aphids); they are also hosts of Calopha ulmicola (Elm Cockscomb Aphid) and Tinocallis ulmifolii (Elm Leaf Aphid). Other insect feeders include Gossyparia spuria (European Elm Scale), Corythucha ulmi (Elm Lace Bug), the plant bugs Lygocoris invitus and Reuteria irrorata, and many leafhoppers (primarily Eratoneura spp. & Erythridula spp.). American Elm is a preferred host plant of the following leafhoppers: Eratoneura affinis, Eratoneura ardens, Eratoneura basilaris, Eratoneura bigemina, Eratoneura bispinosa, and Erythridula obliqua. One species, Scaphoideus luteolus (White-Banded Elm Leafhopper), transmits the virus causing phloem necrosis. The larvae of Saperda tridentata (Elm Borer) and several other long-horned beetles bore through the wood of elms. Two species of bark beetle, Hylurgopinus rufipes (Native Elm Bark Beetle) and Scolytus multistriatus (Small European Elm Bark Beetle), transmit the fungus causing Dutch Elm Disease. Another group of insect feeders include Calligrapha scalaris (Elm Calligrapha), Monocesta coryli (Large Elm Leaf Beetle), and Xanthogaleruca luteola (Elm Leaf Beetle). The Insect Table provides a more complete list of insect species that feed on elms.



Vertebrate animals also use American Elm and other elms as a food source. The following birds eat the seeds or buds of these trees: Wood Duck, Prairie Chicken, Wild Turkey, Carolina Chickadee, Rose-Breasted Grosbeak, Purple Finch, Eastern Goldfinch, House Sparrow, and Yellow-Rumped Warbler. The Yellow-Bellied Sapsucker drills holes through the bark to suck the sap. Among mammals, the Gray Squirrel, Fox Squirrel, Red Squirrel, and Eastern Chipmunk eat the seeds, while the Cottontail Rabbit and White-Tailed Deer occasionally browse on the twigs and foliage. The beaver gnaws on the wood and bark of trees that grow near sources of water. Such birds as the Baltimore Oriole, Warbling Vireo, and Red-Shouldered Hawk use elms as habitat for their nests.

Photographic Location: A woodland opening and woodland border at Busey Woods in Urbana, Illinois.



Comments:
This tree is one of the fallen icons of America, but it still lingers in diminished form. It is a reasonably attractive tree with shiny leaves. In the past, the wood was used to make furniture, flooring, crates, hockey sticks, and caskets. The wood is heavy, hard, and strong, but it lacks durability and has a tendency to warp. American Elm can be distinguished from other elms (Ulmus spp.) by considering the following characteristics: 1) its samaras are ciliate along their margins, otherwise they are hairless, 2) the upper surface of its leaves is largely hairless with a smooth to slightly rough texture, 3) on each side of the central vein of a leaf, there are 0-3 lateral veins that become forked toward the leaf margin, 4) a cross-section of the bark on older trees reveals alternating light and dark layers, and 5) its terete twigs never have corky wings. Other elm trees in Illinois fail to satisfy one or more of the above characteristics.

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