Deciduous, monoecious trees or shrubs with scaly buds. Lvs alternate, simple; stipules usually caducous. Fls wind-pollinated, the sexes in different infls, often produced before the lvs; ♂ fls in pendulous catkins; fls 2-3 in axil of each bract; each group of fls with 2-4 bracteoles; perianth minute, 4-lobed; stamens 2 or 4. ♀ fls in erect catkins; bracts and bracteoles as in male fls; fls 2-3 in axil of each bract; perianth 0. Ovary superior, 2-celled. Styles 2, free. Ovules 1 per cell, pendulous. Fr. a compressed nutlet, usually winged, 1-3 in the axis of scales formed from the fusion of bracts and bracteoles, the whole forming a cylindric, ellipsoid or ovoid cone-like structure. Seed non-endospermic, with straight embryo.