Lysimachia mauritiana is a somewhat fleshy perennial herb that becomes woody at the base. The stems, which are 10–80 cm long, can be either unbranched or branched from near the base and are glabrous. The simple, alternate leaves are spatulate to elliptic, measuring 20–60 cm in length and 5–25 mm in width, with an acute apex and entire margins. The lower surfaces of the leaves are notable for their scattered black glands, and the blades range from chartaceous to slightly fleshy. The upper leaves are sessile, while the lower ones taper into 0–15 mm long petioles. The flowers appear in congested bracteate racemes, elongating post-anthesis to 3–15 cm in length. The flowers are perfect, actinomorphic (radially symmetric), 5-merous, with pedicels 3–20 mm long. The calyx comprises five sepals with lanceolate, deltate, or elliptic lobes, each 4–7 mm long, featuring black glands and scarious margins. The corolla is white or tinged pink, 8–14 mm long, deeply lobed, with elliptic, imbricate lobes. The stamens are as many as and opposite the corolla lobes, with distinct filaments adnate to the lower half of the corolla. The fruit is a 5–6 mm long pyriform capsule, irregularly dehiscent, containing numerous angled, rugulose seeds that are 0.6–0.9 mm long. It is found in coastal rocks, sea cliffs, and gravel beaches between 2–9 meters.