Dioecious trees or shrubs. Growth-mode in flushes. Leaves simple, spirally arranged, mostly elliptic to linear, often deciduous. Stipules mostly caducous, sometimes wanting. Catkins terminal, on short, caducous, axillary axes (bearing dwarfed leaves in Mal. spp.). Flowers about spirally arranged along the rhachis of the catkin, each subtended by a membranous, entire bract. Perianth absent. Disk variable in shape, often consisting of 2 median lobules, or only one adaxial (in extra-Mal. spp. rarely more in a whorl, or cupular). Stamens (1-)2-l5, in Malaysian spp. free or nearly so; anthers dehiscing longitudinally. Ovary more or less stipitate, 1-celled, consisting of 2 carpels; style more or less distinct, lobed. Ovules several, anatropous, basal, inserted amidst a mass of gradually developing, 1-celled hairs on 2 marginal placentas in the lower part of the ovary; the hairs arising both from the funicle and surrounding tissue. Capsule 2-valved, valves recurving. Seeds small, pushed out together with the hairs, without endosperm; testa thin. Distr. About 300 spp., except a few tropical and subtropical ones, restricted to the temperate and cold zones of the N. hemisphere.