Richard K. Rabeler, Ronald L. Hartman

Herbs [small shrubs], winter annual, annual, or perennial; taprooted, not rhizomatous. Stems prostrate to erect, simple or branched. Leaves opposite or sometimes appearing whorled, bases connate or not, sometimes petiolate or often sessile, stipulate; stipules ovate or deltate to lanceolate or bristlelike, scarious; blade subulate or subtriangular to linear and threadlike or spatulate to ovate or orbiculate, seldom succulent. Inflorescences terminal or axillary cymes, or flowers solitary; bracts scarious or absent; involucel bracteoles absent. Pedicels present or flowers sessile. Flowers bisexual or rarely unisexual; perianth and androecium hypogynous or perigynous; hypanthium absent or dish- or cup-shaped; sepals 5, distinct or sometimes connate proximally, hooded (Drymaria, Polycarpon) or not, awned (Polycarpon) or not; petals absent or (3-)5, blade clawed (Drymaria) or not, auricles absent, coronal appendages absent, blade apex entire, erose, or 2(-4)-fid, sometimes emarginate; stamens (1-)3-5(-10), in 1 or 2 whorls, usually arising from base of ovary or from rim of hypanthium (Spergula, Spergularia); staminodes absent; ovary 1-locular; styles 1 or 3, occasionally 2 or 5, distinct or sometimes connate proximally; stigmas 3, occasionally 2 or 5. Fruits capsules, opening by 3 or 5, occasionally 4 valves; carpophore sometimes present. Seeds 3-150+, whitish or tan to often brown or black, ± triangular, pyriform, or reniform to circular, subglobose or laterally compressed to angular (Polycarpon); embryo peripheral, curved or rarely annular to spirally curved (Spergula). x = [7], 8, 9, (11), 12.

Genera 16, species ca. 210 (7 genera, 28 species in the flora): w North America (including Mexico), w South America, Europe (Mediterranean region), Asia (Mediterranean region), Africa (Mediterranean and tropical regions), less diverse in temperate areas.

More commonly recognized as a tribe, Polycarpoideae is characterized by the presence of stipules, well-developed petals, and capsules. It is a relatively small group, with about four-fifths of the species in Drymaria, Polycarpaea, and Spergularia. Although clearly stipulate, Spergularia clusters with members of Alsinoideae in recent molecular studies (M. Nepokroeff et al. 2002; R. D. Smissen et al. 2002).