Alyxia fosbergii is a plant species known only from Henderson Island, one of the Pitcairn Group of Islands in the Pacific Ocean. Henderson Island is an uninhabited raised coral atoll, with an area of 37.3 km2. It has been declared a World Heritage Site by the United Nations. Alyxia fosbergii is a shrub or subshrub, erect or trailing, up to 8 m high with a trunk diameter of 2 cm. Leaves are generally in whorls of 4, lanceolate, up to 8 cm long. Inflorescences are in the axils of the leaves, each with 3-4 orange or salmon flowers about 8 mm long. It is found at elevations of 20–30 m.