Description from Flora of China
Trees deciduous; bark scaly, rough. Buds ovoid, with many overlapping scales. Leaves irregularly and doubly serrate, sometimes lobulate. Male inflorescence pendulous, clustered at apex of branchlets, slender, naked during winter; bracts overlapping, each subtending 1 flower; perianth absent; stamens 3-14; filaments 2-cleft at apex, inserted at base of bracts; anthers each with 2 separate locules, pubescent at apex. Female inflorescence terminal, racemose; flowers paired; bracts overlapping, saccate, inflated, membranous, with reticulate veins and rigid hairs at base, usually lobed at apex; calyx adnate to ovary. Nutlet narrowly oblong, narrowly ovoid, ovoid-ellipsoid, or obovoid, ribbed, completely enclosed in bracts.
About 8 species: China, Japan, Korea; Europe, North America; five species (four endemic) in China.