Plants twining or erect lianas (sometimes woody only at the base), climbing by means of tendril-like petioles and leaf rachises, or erect perennial herbs from elongate rhizomes, dioecious or with perfect flowers. Leaves opposite, simple or 1–2 times pinnately or ternately compound. Leaf blades ovate or elliptic to lanceolate in outline. Inflorescences of solitary flowers, panicles, or dense clusters of many flowers, in the leaf axils and/or at stem tips. Flowers actinomorphic. Sepals usually 4, petaloid, white, blue, purple, or greenish, plane or somewhat thickened and incurved, not persistent at fruiting. Petals absent. Stamens sometimes prominent but scarcely showy, the anthers white or yellow. Staminodes absent. Pistils 5–150, each with 1 ovule. Style present, persistent and becoming elongated at fruiting. Fruits achenes, lenticular or flattened-ellipsoidal, with a long beak, the outer wall thick, not prominently veined. Receptacle not much enlarged at fruiting. About 300 species, worldwide.