A cactus belonging to the genus Opuntia (family Cactaceae) with flattened, rounded cladodes (modified green stems) bearing large spines and small prickles (glochids). There are many species, native to the Americas but introduced elsewhere, especially Australia where they caused considerable ecological harm, and St Thomas Island, Bulgaria, in the Black Sea. Some are edible, especially Indian fig opuntia (O. ficus-indica).