Mats leafy, to 10 cm wide. Stems diffusely branched from base. Leaves: unequal pairs alternating, usually subtending fascicle of leaves; petiole slender, ± equaling blade length; blade apex obtuse; larger blade of pair 0.5(-1.2) cm, smaller blade 0.2(-0.6) mm. Inflorescences: flowers in axils of smaller leaves (bracts) between short lateral stem and main stem; bracteoles 2; pedicel 2 mm. Flowers: calyx lobes erect, ovate, to 1.5 mm, margins scarious, fringed, apex obtuse. Capsules subglobose, membranous. Seeds red-brown, ± round-reniform or subtriangular, asymmetric, 0.3 mm, smooth. Flowering summer-fall. Moist, seasonally flooded, or seasonally dry, open mud or sand flats, banks, shores, and margins of ponds, lakes, canals, and rivers; 0-1000 m; introduced; Ariz., Calif., Fla., La., Miss., Nev.; West Indies; South America.

Plant: Annual, mat-forming, glabrous; stem prostrate, slender, diffusely branched from base, forming leafy mats < 10 cm Leaves: of a pair unequal, opposite; stipule sheathing stem, scarious, fringed, attached to lower petiole margins; petiole ± = blade; larger blades 5-10 mm, elliptic, obtuse; axil of smaller leaf with short stem, flower, or both INFLORESCENCE: flower solitary in axil; bracts fringed Flowers: ± 2 mm diam; calyx bell-shaped, lobes 4-5, unequal, calyx lobes ± 1.5 mm; erect, ovate, margin scarious; ovary superior, ovoid to round, chamber 1, placenta free-central; styles and stigmas generally 2 Fruit: ± round capsule, circumscissile, thin-walled; seeds many, ± 0.3 mm, round-reniform, smooth, brown; aril slender, persistent on placenta Misc: Seasonally dry margins of wetlands; < 1000 m.