Ash (tree)

Ash (tree), common name for a group of plants belonging to the olive family, valued for timber and ornament. Characteristic of the group are the small, inconspicuous greenish flowers, usually borne in clusters with or without sepals and petals. These appear in early spring and produce dry, single-winged fruits called samaras. The finely toothed leaves are opposite on the stems and are compound, bearing an odd number of leaflets. The white, or American, ash; European ash; and Siebold ash of Asia are particularly valuable sources of woods used in cabinetry. The flowering, or manna, ash, notable for its long petals, is cultivated in Mediterranean regions for its sweet gum (see Manna).

In recent years, ash trees in North America have been devastated by a beetle known as the emerald ash borer. Native to Japan, Korea, and parts of Russia and China, the metallic-green insect was accidentally introduced to North America during the 1990s. It first infected ash trees in Michigan but has since spread to other Midwestern and north central states, and into Canada. The beetle larvae bore under the bark of trees and feed on the inner bark and phloem, interfering with the tree’s ability to take in and transport water and nutrients.

Mountain ash is an unrelated tree of a different family (see Rose). The prickly ash, also called Hercules’-club, also belongs to a different family (see Rue).

Scientific classification: Ash trees constitute the genus Fraxinus, of the family Oleaceae. The white, or American, ash is classified as Fraxinus americana; the European ash as Fraxinus excelsior; the Siebold ash as Fraxinus sieboldiana; and the flowering, or manna, ash as Fraxinus ornus. The mountain ash belongs to the family Rosaceae, and the prickly ash to the family Rutaceae.