Herbs, annual, with long-trailing, decumbent shoots. Leaves: blade linear-oblong to linear-lanceolate, 1.5–7 × 0.2–1 cm, glabrous. Inflorescences terminal and in distal leaf axils; cymes 1-several, 1-flowered, solitary or fascicled. Flowers bisexual, radially symmetric, 1 cm wide; sepals 5–6 mm; petals purplish lilac or purple to pink or white, 5–8 mm; stamens 3; filaments bearded; staminodes 3. Capsules (4–)5–9 mm. Seeds 2–6 per locule, 1.6–3 mm, faintly ribbed.
Phenology: Flowering fall.
Habitat: Roadside ditches and swales, margins of lakes, creeks, rivers, swamps, bogs, swamp forest, and other aquatic habitats, often growing in water
Introduced; Ark., Fla., Ga., Ky., La., Md., Miss., N.C., Oreg., S.C., Tenn., Va., Wash., Europe, native, Asia.
I agree with C. P. Dunn and R. R. Sharitz (1990) that this species is still expanding its range since its introduction early this century.