Alluaudia is a genus of six species of flowering plants endemic to Madagascar, where they form an important component of the Madagascar spiny forests. They are spiny succulent shrubs and trees from 2-20 m tall, with leaves that are deciduous in the long dry season. The leaves are in pairs, 0.5-3.5 cm long, with one or two thorns 2-2.5 cm long in the axil of each pair of leaves.