Portulaca villosa is a perennial herb with prostrate to weakly ascending stems reaching about 30 cm long. The roots are fleshy and tuberous, becoming woody over time. The leaves are simple and can be alternate or opposite, with narrowly oblanceolate to linear, subterete blades that are 5–25 mm long and 1.5–3 mm wide. The surfaces are pale grayish green, with the upper leaves occasionally involucrate around the flowers. The leaves are succulent, with a dense tuft of yellowish-brown hairs (1–)3–12 mm long in the axil, and have entire margins. The leaves are sessile, and there are two stipules, which are connate basally. The flowers are arranged in dense, terminal, head-like cymes, with 3–6 flowers subtended by dense tufts of hairs 6–12 mm long and a series of involucrate leaves. The bracteoles are about 1.4–1.5 mm long. The flowers are bisexual (perfect), rarely unisexual, actinomorphic (radially symmetric), rarely slightly irregular, and sessile or subsessile. The calyx consists of 2 sepals that are imbricate, persistent, 4–5 mm long, and have scarious margins. The corolla has 4–6(–8) petals that are white, pink, or pink with a white base, obovate, 8–10 mm long, distinct or connate at the base, imbricate, with an emarginate apex. There are 18–50 stamens, with usually puberulent filaments and dithecal anthers that open by longitudinal slits. The ovary is partly inferior, 2–3(–9)-carpellate, soon becoming 1-celled, with numerous ovules and free-central placentation. The styles number 2–9 and are 5–7(8)-branched. The fruit is a membranous, broadly ovoid capsule, 3–5 mm long, with thin walls about 0.05 mm thick, and is circumscissile near the base up to one-third from the base. The seeds are dark reddish-brown, 0.6–0.7 mm long, with a stellulate-rugulose surface. It is found in dry, rocky, clay, lava, or coralline reef sites between 0-300 meters, occasionally up to 490 meters.