Elm

Elm, common name for trees and shrubs of a family widespread throughout the North Temperate Zone. The tall, deciduous trees of the representative genus have straight-veined elliptic leaves. The purple or yellowish flowers bloom in clusters and appear before the leaves unfold.

The most common and most popular of the North American elms is the American elm, a tree valued for its ornamental shade qualities, which often grows to 37 m (120 ft). Five other species from which numerous horticultural varieties have been developed, are native to the United States. The Chinese elm is a small half-evergreen tree, frequently planted in the South and in California. The red (or slippery) elm is a common species of medium height. The rock (or cork) elm, valued for its corky, winged twigs, is hardy in the New England area and northern portions of the United States. The wahoo (or winged) elm, is a small tree found primarily in Florida, Louisiana, and Arkansas.

Another important species of elm is the English elm, which grows up to 30 m (100 ft) high; occasional specimens are much taller. Found throughout western Asia, Europe, and northern Africa, it has been introduced into the United States and planted along the streets of many cities. The wood is compact, durable, and water resistant and is used for the manufacture of numerous items. The outer bark is used medicinally; dyes are also made from it. Also in the family, the hackberry genus contains about 80 species of trees and shrubs, some of which produce edible fruits.

In recent years the elm population in the United States has been markedly decreased by Dutch elm disease. The disease was introduced into the United States accidentally from the Netherlands. Although Dutch elm disease can not be eliminated, effective control programs can slow the spread of the disease and greatly reduce the loss of trees. Several disease-resistant varieties of elm have also been developed.

Elm trees are also frequently destroyed by insects that feed on their foliage. Examples of these insects include the gypsy moth, the tussock moth, and the bagworm. The elm-leaf beetle is perhaps the most destructive to the foliage of the elm. It is a small yellowish-brown beetle, which begins to feed while the leaves are still young, eating large, round holes into them. The adult elm-leaf beetle deposits clusters of eggs on the undersides of the leaves and dies soon thereafter. The larvae feed voraciously on the leaves. Phloem necrosis, another serious disease, is caused by a virus carried by an insect, the leafhopper.

Japanese zelkova, an elm species resistant to Dutch elm disease, has replaced the American elm as an ornamental tree in many areas of the United States. The name elm is also applied in Australia to a tall shrub of the nightshade family.

Scientific classification: Elms make up the family Ulmaceae. The American elm is classified as Ulmus americana, the Chinese elm as Ulmus parvifolia, and the red (or slippery) elm as Ulmus rubra. The rock (or cork) elm is classified as Ulmus thomasii, the wahoo (or winged) elm as Ulmus alata, and the English elm as Ulmus procera. The hackberry genus is Celtis. The Japanese zelkova is classified as Zelkova serrata and the tall shrub of Australia of the family Solanaceae as Duboisia myoporoides.