ash, in botany, any plant of the genus Fraxinus of the family Oleaceae (olive family), trees and shrubs mainly of north temperate regions. The ashes are characterized by small clusters of greenish flowers and by fruits with long “wings” to aid in wind dispersal. The most valuable of the North American species used for hardwood timber is the white ash (F. americana), ranging from Nova Scotia to Minnesota and Texas. Its strong, durable wood is used for sporting goods, furniture, tool handles, and oars. The bark of the blue ash (F. quadrangulata), which is found from the S Midwest to Oklahoma and Tennessee, yields a blue dye. Both the white ash, blue ash, and other North American species as well as the European ash (F. excelsior) are threatened by the emerald ash borer, a beetle native to Asia whose larvae kill ash trees by boring under the bark and into the wood, cutting off the flow of nutrients. Ash dieback, in which crown dieback and leaf loss results from infection with the fungus Hymenoscyphus fraxineus, also is a threat to the European ash. The Mediterranean flowering ash (F. ornus) is the source of commercial manna. The name flowering ash is also applied to a shrubby species (F. cuspidata) of the California canyon chaparral and to the fringe tree (genus Chionanthus of the same family) of North America and China. The mountain ash and prickly ash are not true ashes. Ashes are classified in the division Magnoliophyta, class Magnoliopsida, order Scrophulariales, family Oleaceae.
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