ACERACEAE

the maple family of flowering plants, in the order Sapindales, comprising about 200 species of trees and shrubs in two genera, Dipteronia (two species) of central and southern China, and Acer, the maples, widely distributed in the Northern Hemisphere, crossing the equator only in Malaysia. In Dipteronia the seed is surrounded by a wing; in Acer it is winged only on the back. Leaves of maples are opposite, simple, or compound (divided into separate leaflets) and usually toothed or lobed. The small, clustered flowers are mostly unisexual and are sometimes without petals. The fruit, a samara (a winged nutlet), splits into two (rarely three) winged, one-seeded parts. Many maples are cultivated for ornament and shade. Maples have a watery, sweet sap that in some species, especially sugar maple (A. saccharum), is used to make syrup and sugar. Certain species of Acer are also important timber trees. See also box elder; maple.