Annual or perennial, fibrous herbs or subshrubs, sometimes provided with stinging hairs. Leaves simple, alternate or opposite, those of a pair often unequal. Stipules present or rarely wanting. Inflorescence consisting of bracteated cymes, pseudo-spikes or pseudo-heads, sometimes flowers solitary; cymes borne on a short or elongate axis arising from the upper leaf-axils. Flowers unisexual or rarely hermaphrodite, small, actinomorphic. Tepals (2—)4—5, free or connate. Male flowers: stamens as many as the tepals, epitepalous; filaments free, curved inwards in bud and springing back elastically at anthesis; anthers 2-celled, with longitudinal dehiscence; ovary rudimentary or wanting. Female flowers: scale-like staminodes often present at the base of the ovary; ovary superior or inferior, unilocular; style 1; stigma 1; ovule one, basal. Fruit a drupe or achene, often enclosed by the persistent perianth. Embryo straight. Endosperm present or wanting. Cotyledons thick and flat. Nearly 700 species in about 42 genera, mostly tropical and subtropical, especially in the New World.