Description from Flora of China
Trees or rarely shrubs, deciduous. Bark furrowed. Axillary buds of most apical leaves in false-terminal buds, usually enclosed by 2 outer scales, imbricate within. Leaves spirally arranged but twisted and appearing 2-ranked; secondary veins ± parallel. Male inflorescences erect catkins; flowers in clusters of 1-3(-5) with each cluster subtended by a bract; perianth 6-parted; stamens 10-12(-20); rudimentary pistil pubescent. Female flowers borne on proximal part of androgynous inflorescences, rarely on a separate inflorescence, usually 3 and subtended by 1 symmetric cupule; ovary 6-9-loculed; styles 6-9; stigmas terminal, minutely punctiform. Cupules splitting into 2-4 valves; bracts spinelike. Nuts 1-3 per cupule. Germination hypogeal.
About 12 species: Asia, Europe, North America; four species (two endemic, one introduced) in China.
Most species are cultivated for edible nuts and durable wood.