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ELM - 5 reference results

elm, common name for the Ulmaceae, a family of trees and shrubs chiefly of the Northern Hemisphere. Elm trees (genus Ulmus) have a limited use as hardwoods for timber, especially the rock or cork elm (U. thomasi). Tall and graceful, with fan-shaped crowns of finely subdividing branches and twigs, elms are widely planted as ornamental and shade trees, chiefly the American, or white, elm (U. americana) and the English, or Wych, elm (U. campestris) of N and central Europe and W Asia. Tolerant of urban conditions, both species are among those plants attacked by the fungus known as Dutch elm disease (see fungal infection), but disease-tolerant varieties have been propagated. The mucilaginous inner bark of the slippery elm (U. fulva) is used medicinally in cough drops. Some species of the genus Celtis (the hackberries of America and the nettle trees of the Old World) are cultivated for their edible fruit. False sandalwood (Planera aquatica) is a member of the elm family; its fragrant wood is used in cabinetmaking. The elm family is classified in the division Magnoliophyta, class Magnoliopsida, order Urticales.

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Dutch elm disease

Dutch elm disease: see diseases of plants; elm.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

elm

Leaves and fruit of an American elm tree.

Any of about 18 species of forest and ornamental shade trees that make up the genus Ulmus (family Ulmaceae), native mostly to northern temperate areas. Many are grown for their height and attractive foliage. The leaves are doubly toothed and often lopsided at the base. The flowers, which lack petals, appear before the leaves and are borne in clusters. Seeds are borne in a samara (dry, winged fruit). The American elm (U. americana) has dark gray, ridged bark and elliptical leaves. Many species are susceptible to Dutch elm disease. Elm wood is important for boats and farm buildings because it is durable in water; it is also used for furniture. Seealso slippery elm.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Dutch elm disease

Widespread disease that kills elms, originally described in The Netherlands. The disease is caused by the fungus Ophiostoma ulmi (also known as Ceratocystis ulmi). It was first identified in the U.S. in 1930, and an eradication campaign could not stop its spread into regions wherever the very susceptible American elm (Ulmus americana) grew. The leaves on one or more branches of a stricken tree suddenly wilt, turn dull green to yellow or brown, curl, and may drop early. Because symptoms are easily confused with other diseases, positive diagnosis is possible only through laboratory culturing. The fungus can spread up to 50 ft (15 m) from diseased to healthy trees by natural root grafts. Overland, the fungus normally is spread by the European elm bark beetle (Scolytus multistriatus; see bark beetle), less commonly by the American elm bark beetle (Hylurgopinus rufipes). Control involves exclusion of the beetles, usually by use of an insecticidal spray applied to the tree.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.