Herbs annual. Stems creeping, branched (sometimes at every node), to more than 1 m, glabrous or hispidulous throughout or in a line. Leaves subsessile; leaf sheath hispid or hispid-ciliate, with red lines; leaf blade lanceolate or proximal ones oblong, 3--12 × 0.8--3 cm, glabrous or hispid. Involucral bracts borne opposite leaves, folded, ovate-lanceolate, 1--4 cm, glabrous or hispidulous abaxially, base cordate or rounded, apex acuminate or shortly so. Cincinni dichotomously branched from base; 1 branch with 1.5--2 cm long peduncle and 1--4 long-exserted male flowers; other branch with much shorter peduncle and 3--5 bisexual flowers included in involucral bracts; pedicels thick and curved, ca. 3 mm, to 5 mm in fruit. Sepals 3--4 mm, membranous. Petals blue, 2 longer ones 4.2--6 mm. Capsule oblong, trigonous, ca. 5 mm, 3-valved; posterior valve with 1 seed, indehiscent; other 2 valves each with 2 seeds, dehiscent. Seeds black, ovoid-globose, ca. 2 mm, reticulate. Fl. May--Nov.

A medicinal herb with febrifugal and diuretic effects. The petal juice can be used as a dye for painting.

Forests, thickets, streamsides, humid open places; near sea level to 2100 m. Guangdong, SW Guangxi (Longzhou Xian, Pingxiang Shi), SW Guizhou (Anlong Xian, Wangmo Xian), Hainan, SE Xizang (Mêdog Xian), SE Yunnan [tropics and subtropics worldwide].