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Contains 6 genera and about 150 species of trees and shrubs, primarily in cooler portions of the Northern Hemisphere. Leaves are simple, deciduous, alternate; species monoecious; flowers in aments. Staminate aments are preformed (except for Carpinus). Fruit is a small nut, subtended by a papery or semi-woody involucre (cluster of bracts); ripens in autumn (except for Betula nigra).