Sesuvium portulacastrum is a succulent herb or subshrub. The stems are red to green, decumbent to ascending, fleshy, many-branched, glabrous, and often root at the nodes. The leaves are simple and opposite. The blades are linear, elliptic to narrowly obovate, 1–4(–6) cm long, and 0.2–1.5 cm wide. They can be cylindrical (terete) or flattened. The apex is rounded to acute and gradually tapers to the base, which is dilated and clasping, with the bases of paired leaves often overlapping. The surfaces are glabrous or pubescent with bladder-like hairs, and the leaves are green, often becoming yellow or red with age. The margins are entire. Petioles and stipules are absent. The flowers are solitary in the leaf axils and bisexual (perfect). The calyx has five sepals, connate at the base. The calyx lobes are green externally and pinkish purple to white within. They are lanceolate to narrowly ovate, 4–10 mm long, 3–6 mm wide, with a green, subapical, dorsal appendage 1–1.5 mm long, and the tube is 1.5–3 mm long. The corolla (petals) is absent. Stamens are numerous and pinkish purple. The ovary is partly superior and 3-celled, with three styles. The fruit is a capsule with circumscissile dehiscence, ovoid to subglobose, 4–7 mm long, on pedicels 2–12 mm long. Each capsule contains 10–30 lenticular–reniform seeds, 1–1.5 mm in diameter, with a smooth and lustrous surface. The perisperm is oily, starchy, or proteinaceous; true endosperm is absent. It occurs in coastal habitats at 0-50 meters.