Portulaca lutea is a prostrate to weakly ascending perennial herb. The older stems have a thin, pale, corky secondary growth layer. The leaves are simple, alternate to subopposite, with obovate to orbicular blades measuring 10–25 mm long and 7–15 mm wide. The upper leaves occasionally form an involucre around the flowers. The leaves are succulent, with a tuft of hairs up to 6 mm long in the axil. The leaf margins are entire, and the leaves are petiolate. There are two stipules, which are connate basally. The flowers are 1–3 in terminal, congested cymes on leafy or short leafless internodes that are 0.5–3 cm long. The flowers are bisexual (perfect), actinomorphic (radially symmetric), or rarely slightly irregular, sessile, or subsessile. Each flower is subtended by bracteoles about 4 mm long and hairs about 2 mm long. The calyx consists of 2 sepals, which are imbricate, persistent, suborbicular, about 7–9 mm long, with a fleshy center and a keel about 4 mm long. The corolla has 4–6(–8) petals that are yellow, broadly obovate to obovate, about 10–12 mm long, distinct or connate at the base, imbricate, with an emarginate to mucronate apex. There are 12–50 stamens with about 4 mm long filaments, usually puberulent. The anthers are yellow to red, dithecal, and open by longitudinal slits. The ovary is partly inferior, 2–3(–9)-carpellate, soon becoming 1-celled, with free-central placentation and numerous ovules. The styles number 2–9. The fruit is a membranous capsule, ovoid, about 7 mm long, and circumscissile, about one-third from the base. The seeds are about 1 mm long, and the seed coat cells are smooth to tessellate or slightly tuberculate. It is found in coastal and strand habitats, such as lava, raised coralline reefs, dunes, and soil pockets or cracks between 0-40 meters.