Annual, aquatic or semiaquatic, erect or decumbent small herb; lower branches smooth or thinly pubescent, often swollen at nodes; leaves opposite, sessile, linear to elliptic or oblanceolate with sharp, acute apex, margins serrulate; stipules triangular-lanceolate, acute, serrate with gland tipped teeth, pubescent; inflorescence subverticillate or in dense, axillary fascicles; flowers minute, subsessile or shortly pedicelled, covered with glandular or eglandular hairs; sepals 5, lanceolate, acute, scarious, denticulate, often reddish pink; petals 5, stamen 3-5, free, anthers versatile; ovary ovoid, oblong, deeply grooved styles 5, stigma globose; capsule ovoid, 3-6-valved, margins of the valves slightly incurved, dehiscing from the central axis; seeds numerous, ovoid, sometimes slightly curved.