Herbs annual. Stems sometimes flushed red or purple, not articulated, prostrate or decumbent, less often ± erect, diffuse, much branched; leaf axils with a few inconspicuous stiff bristles. Leaves alternate or occasionally subopposite; petiole short; leaf blade flat, obovate, 10-30 × 5-15 mm, base cuneate, apex obtuse, rounded, truncate, or retuse. Flowers in clusters of 3-5, 0.4-0.5 cm in diam., surrounded by involucre of 2-6 bracts. Sepals green, helmeted, ca. 4 mm, apex acute, keeled. Petals 5, yellow, obovate, 3-5 mm, slightly connate at base, apex retuse. Stamens 7-12, ca. 12 mm; anthers yellow. Ovary glabrous. Stigma 4-6-lobed. Capsule ovoid, ca. 5 mm. Seeds glossy black when mature, never iridescent, obliquely globose-reniform, 0.6-1.2 mm; testa cells stellate, usually with central peglike tubercle, sometimes without and then surface ± granular. Fl. May-Aug, fr. Jun-Sep.
Cultivation, disturbed urban sites. Throughout China [tropical and temperate regions worldwide].
Danin et al. (Israel J. Bot. 27: 177–211. 1978) recognized a series of eight subspecies, but they are rather poorly correlated with geography and their status needs re-evaluation. The Chinese material seems to belong to the most common and weedy form placed in subsp. oleracea. There has been some selection of more robust forms for use as a vegetable; these are sometimes placed in subsp. sativa (Haworth) Celakovský.
The plants, which are common weeds of cultivation, are eaten as a vegetable and used for medicinal purposes.