Description from Flora of China
Hedyotis herbacea Loureiro (1790), not Linnaeus (1753); Oldenlandia diffusa (Willdenow) Roxburgh; O. herbacea (Linnaeus) Roxburgh var. uniflora Bentham.
Slender herbs, annual, ascending to procumbent, to 50 cm tall; stems slightly flattened to terete or young stems sometimes 4-angled, sparsely to densely puberulent, scaberulous, or glabrescent to glabrous, similarly glabrous or pubescent on angles and to sides. Leaves sessile or subsessile; blade drying membranous, linear, narrowly elliptic, or narrowly oblanceolate, 1-4 × 0.1-0.4 cm, adaxially glabrous and smooth or often scaberulous near margins, abaxially glabrous to scaberulous, base acute, margins usually revolute at least when dry, apex acute; secondary veins not visible; stipules fused to petiole bases, triangular to truncate, 0.5-1.5 mm, glabrescent, acute to aristate or with 1-3 bristles 0.2-1 mm. Inflorescences axillary, 1-flowered or fasciculate and 2-flowered, glabrous, pedunculate; peduncles or pedicels 4-20 mm; bracts none or stipuliform, to 1 mm. Flowers pedicellate, apparently homostylous. Calyx glabrous; hypanthium portion subglobose, 1-1.2 mm; limb lobed essentially to base; lobes narrowly triangular, 1-2 mm, ciliolate. Corolla white, tubular, outside glabrous; tube 1.5-2.5 mm, glabrous inside; lobes ovate-oblong, 1.2-2 mm. Anthers ca. 0.8 mm, exserted. Stigma ca. 1.2 mm, exserted. Fruit capsular, compressed globose to oblate, 2-3 × 2-3 mm, sometimes somewhat dicoccous, membranous, glabrous, loculicidally dehiscent on flat to beaked top, beak rounded, to 0.5 mm, with peduncles elongating rapidly and markedly as fruit mature, to 20 mm; seeds ca. 20, dark brown, angled, deeply thickly foveolate. Fl. and fr. May-Oct.
This species is very commonly collected in China. The taxonomy of this and related species is complicated, and different authors have drawn very different conclusions (e.g., Sivarajan & Biju, Taxon 39: 665-674. 1990; Dutta & Deb, Taxon. Rev. Hedyotis. 2004). In particular, Hedyotis brachypoda, H. corymbosa, and H. erecta are related and have been variously circumscribed. Here, these species are circumscribed generally, though not completely, following W. C. Ko (in FRPS 71(1): 72, 75. 1999) and Dutta and Deb.
Paddy fields, ridges of farmlands, humid open fields; sea level to 900 m. Anhui, Fujian, Guangdong, Guangxi, Hainan, Taiwan, Yunnan, Zhejiang [Bangladesh, Bhutan, Indonesia, Japan, Malaysia, Nepal, Philippines, Sri Lanka, Thailand].