Description from Flora of China
Herbs annual or perennial. Stems prostrate or decumbent; nodes or leaf axils with scales, bristles, and/or hairs, sometimes short and inconspicuous. Leaves alternate or opposite, usually sessile, flat or terete. Inflorescence a terminal head of sessile, solitary or clustered flowers, subtended by an involucre of leaves. Sepals connate at base into tube, persistent but inconspicuous. Petals 4 or 5(-8+), free or shortly connate at base. Stamens 4-100, adnate to base of petals. Ovary half-inferior. Stigma 2-9-lobed. Capsule circumscissile, sessile, globose or nearly so. Seeds mostly glossy black or iridescent gray, less often brown, orbicular-reniform, minute, often tuberculate, without caruncle.
Portulaca grandiflora Hooker, a native of South America, is cultivated in China as a popular garden flower. Outside the Flora area it is known to escape from cultivation. It is easily recognized by the terete leaves and large flowers, 2.5–4 cm wide, which often have more than five petals that can be red, purple, yellow, or white.
About 150 species: more arid tropical and subtropical regions, particularly Africa and South America, a few species extending into temperate regions; five species (two endemic, one introduced) in China.