in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. 67[IV,3b]: 76. 1891.
Annuals or perennials. Stems erect, 15–40 cm, hairy, glabrescent. Leaves hairy, glabrescent; blade base narrowly cuneate, margins entire, apex rounded. Pedicels 1.5–15 mm. Flowers: sepals 4(or 5), oblong to lanceolate, calyx bilaterally symmetric; corolla pink with pink throat or white with white throat, 2–5 mm; stamens 4, didynamous. 2n = 28.
Phenology: Flowering Jul–Sep.
Habitat: Muddy sites, pools, rice fields.
Elevation: 0–100 m.
Introduced; Calif., Fla., La., S.C., Tex., West Indies (Greater Antilles, Lesser Antilles, Puerto Rico), Central America, introduced also in Mexico, South America (Colombia), Asia (China).