Annual or perennial herbs or shrubs, usually pubescent, frequently with stinging hairs. Leaves alternate or opposite, simple, usually stipulate. Flowers unisexual, rarely hermaphrodite (plants monoecious, dioecious or poly- gamous), small, crowded in cymes. Perianth sepaloid, free or united. Staminate flowers with (1-)4-5 stamens opposite the perianth segments, mostly bent inwards in bud and exploding at flowering; anthers 2-celled, opening lengthwise; rudimentary ovary often present. Pistillate flowers often with small staminodes, with a 1-celled, 1-ovuled ovary; style simple or 0. Fruit an achene. Seeds with oily endosperm; embryo usually straight.