Herbs annual, glabrous. Stems tufted, slightly diffuse, ascending, 15--25(--35) cm tall, much branched. Leaves sessile, lanceolate to oblong-lanceolate, (0.2--)0.5--2 cm × (1--)2--4 mm, basally sparsely ciliate, both surfaces slightly pinkish green, base cuneate, semiclasping, margin cartilaginous, slightly undulate, apex acuminate. Flowers 3--5 in cymes or solitary, terminal or axillary. Pedicel 0.5--2 cm, slender, glabrous, slightly declinate in fruit. Sepals 5, lanceolate, 2--4 × ca.1 mm, glabrous, midvein raised, margin membranous, apex acuminate. Petals 5, shorter than or subequaling sepals, 2-cleft nearly to base; lobes linear, apex obtuse. Stamens 5(--10), slightly shorter than petals. Ovary ovoid; styles 3, sometimes 2, linear, short. Capsule ovoid-orbicular, subequaling or slightly longer than persistent sepals, 6-valved. Seeds numerous, brown, reniform, slightly compressed, rugulose. Fl. May--Jun, fr. Jul--Aug. 2n = 24, 26, 46.

Fields, streamsides, wetlands; 500--4000 m. Anhui, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Henan, Hunan, Jiangsu, Jiangxi, Nei Mongol, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Bhutan, India, Japan, Kashmir, Korea, Nepal, Pakistan, Vietnam; Europe].