Description from Flora of China
Annuals, 15-25 cm tall. Stems erect or ascending, simple or much branched, glabrous or hispidulous. Leaves opposite, sessile or base narrowed and appearing stalked; leaf blade linear-elliptic, 0.5-3 cm X 3-8 mm, glabrous, margin crenate and toothed, veins pinnate. Flowers solitary and axillary or in axillary or terminal racemes. Pedicel 2-4 mm, glabrous or hispidulous, recurved in fruit. Bracteoles linear, 0.5-0.8 mm. Calyx 4-5 mm, glabrous, with raised veins in fruit. Corolla white or pink, 6-7 mm, outside glabrous. Capsule ovoid, ca. 3.5 mm. Fl. and fr. Jul-Oct.
Wet grassland, near water; below 1500 m. Guangdong, Yunnan [Indonesia, Malaysia, Myanmar, Thailand, Vietnam].