Trees and shrubs with deciduous or persistent alternate petioled lvs. and small mostly deciduous stipules. Plants monoecious; flowers apetalous, the male in catkins or capitate clusters, the female solitary or in small clusters and subtended by an invol. of +/- consolidated bracts, which become indurated and form a cupule partly or completely enclosing the 1-locular and 1-seeded nut. Calyx of male fls. 4-7 lobed; stamens 4-20. Calyx of female fls. 4-8 lobed, adnate to the 3-7 locular ovary. Ovules 1-2 in each locule, usually only 1 ripening; styles 3. Endosperm none; cotyledons large, fleshy. Five genera and about 400 species, mainly of Northern Hemisphere. (Munz, Flora So. Calif. 478).