Sp. Pl. 1: 223. 1753.
Gen. Pl. ed. 5, 105. 1754.
Herbs [shrubs], annual or perennial, glabrous, hairy, or papillate. Roots fibrous. Stems usually prostrate, spreading, branched from base, sometimes woody. Leaves cauline, subopposite, petiolate, those of each pair unequal; stipules attached to margin of petiole, bidentate, usually papery; blade terete or flat, linear to orbiculate, base tapered, margins entire. Inflorescences axillary, flowers solitary or in cymes; bracts foliaceous; bracteoles 2. Flowers inconspicuous, 4 mm diam.; calyx lobes 5, adaxial surface colored, with subapical, abaxial, mucronate appendages; petals and petaloid staminodia absent; stamens perigynous, 5–10[–20], when 5, alternating with calyx lobes; pistil 2-carpellate; ovary superior, 1–2-loculed; placentation basal; ovules 1–12; styles 1–2, longitudinally papillate; stigmas 2. Fruits capsules, dehiscence circumscissile near base; operculum flat, ovoid, or globose, winged or mucronate. Seeds 1–12, brown to black, ridged, triangular, globose, or reniform, smooth or papillate; arils elongate.
North America, Mexico, West Indies, Central America, South America, Asia, Africa, Australia.
Species 20 (1 in the flora).