Shrubs and trees , 3--15 m; tree trunks usually 1, branching mostly deliquescent, trunks and branches terete. Bark grayish brown, thin, smooth, close, breaking into vertical strips and scales in age; prominent lenticels absent. Wood nearly white to light brown, moderately hard, heavy, texture fine. Branches, branchlets, and twigs nearly 2-ranked to diffuse; young twigs differentiated into long and short shoots. Winter buds sessile, broadly ovoid, apex acute; scales several, imbricate, smooth. Leaves on long and short shoots, 2-ranked. Leaf blade broadly ovate with 8 or fewer pairs of lateral veins, 4--12 × 3.5--12 cm, thin, bases often cordate, margins doubly serrate, apex occasionally nearly lobed; surfaces abaxially usually pubescent, sometimes glandular. Inflorescences: staminate catkins on short shoots lateral on branchlets, in numerous racemose clusters, formed previous growing season and exposed during winter, expanding well before leaves; pistillate catkins distal to staminate catkins, in small clusters of flowers and bracts, reduced, only styles protruding from buds containing them at anthesis, expanding at same time as staminate. Staminate flowers in catkins 3 per scale, congested; stamens 4, divided nearly to base to form 8 half-stamens; filaments very short, adnate with 2 bractlets to bract. Pistillate flowers 2 per bract. Infructescences compact clusters of several fruits, each subtended and surrounded by involucre of bracts, bracts 2, hairy [spiny], expanded, foliaceous, sometimes connate into short to elongate tube. Fruits relatively thin-walled nuts, nearly globose to ovoid, somewhat laterally compressed, longitudinally ribbed. x = 11.
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Shrubs or trees deciduous. Leaves alternate, petiolate, margin doubly serrate or lobulate. Male inflorescence pendulous, subsessile, cylindric, spicate-cymose, naked during winter, with numerous overlapping bracts; bracts each usually subtending 2 bracteoles and 1 male flower; stamens 2-8, inserted at middle part of bracts; anthers with 2 separate thecae, often pubescent at apex. Female inflorescence a compact cluster of several flowers; bracts campanulate or forming a tubular sheath, apex usually lobed; flowers paired, enclosed by a bract; calyx adnate to ovary, 4-8-lobed at apex; ovary with 1 or rarely 2 ovules in each cell; style 2-cleft to base. Fruit a subglobose or ovoid nut, enclosed or surrounded by enlarged bracts.
Staminate catkins emerging in autumn, reaching anthesis in early spring, each scale subtending a pair of small bractlets and a single naked fl with 4 stamens, the filaments deeply bipartite, each segment bearing a half-anther; pistillate catkins small, ovoid, the few, closely imbricate scales concealing the fls except for the elongate stigmas, each fl subtending by a minute bract and 2 bractlets, these greatly accrescent at maturity and enclosing the hard-shelled, edible nut; shrubs or small trees with doubly serrate lvs, colonial by roots. 10+, N. Temp.
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