Plants annual, 4--20(--30) cm tall. Stems usually many, erect or ascending, usually weak, base often reddish brown. Leaves basal and cauline; leaf sheath often swollen basally, margin hyaline; leaf blade flat, 1--13 cm × ca. 1 mm, margin often slightly convolute. Inflorescences usually lax, 1/4--4/5 × plant height; branches few, ascending, somewhat arcuate, usually weak, few flowered. Flowers subterminal, remote, appressed to subappressed; involucral bract leaflike. Bracteoles 2 or 3, 1.3--2.5 × 1.2--2.2 mm. Perianth segments lanceolate; outer segments 4.25--5.5 × 1--1.8 mm, center green, margin broadly white membranous, apex sharply pointed; inner segments 4--5 mm, often mostly membranous, apex acute. Stamens 6, 1/3--1/2 as long as perianth; filaments 0.8--1.2 mm; anthers 0.5--0.8 mm. Style absent; stigmas ca. 0.5 mm. Capsule ovoid to subellipsoid, 3--4(--5) mm, 3-loculed, apex slightly obtuse. Seeds ellipsoid, 0.4--0.6 mm, striate, base and apex usually apiculate. Fl. May--Jul, fr. Jun--Sep. 2 n = 100, 110.

Wet grasslands, swamps, lakesides, river banks, streamsides; 100--3500 m. Anhui, Fujian, Gansu, Guizhou, Hebei, Heilongjiang, Henan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, Xizang, Yunnan, Zhejiang [Afghanistan, Bhutan, India, Japan, Kazakhstan, Korea, Mongolia, Nepal, Pakistan, Philippines, Russia, Sikkim, Sri Lanka, Thailand, Vietnam; SW Asia, Europe, North and South America].