Description from Flora of China
Herbs perennial. Stems prostrate, forming mats, much branched, rooting at nodes. Leaves distichous, gradually becoming smaller distally along flowering shoots; leaf blade ovate to lanceolate, 1--4 × 0.6--1.2 cm, glabrous except for scabrid margin and apex, base clasping, subcordate or obtuse, apex acuminate. Inflorescence of paired (sometimes solitary), sessile, dense cincinni in axils of distal leaves. Flowers bisexual or male. Sepals green, linear-oblong, 3--4 mm, hirsute along midvein, margin scarious. Petals white, lanceolate, 3--6 mm. Stamens 3; filaments long exserted; connectives broadly deltoid. Ovary oblong, subtrigonous, 2-loculed, apex pilose; ovules 2 per locule. Style filiform, long; stigma penicillate. Capsule oblong, ca. 1.5 mm, 2-valved. Seeds 2 per valve, brown, ca. 1 mm, rugose. 2 n = 12.
Naturalized on roofs of houses. Hong Kong [native to America, from S United States to Argentina].