OPUNTIA

largest cactus genus of the family Cactaceae, native to the New World and featuring the characteristic glochidiasmall bristles with backward-facing barbs. The genus is divided into subgroups based on the form of the stem segments. Opuntias that have cylindrical joints are called chollas (see cholla); the remaining Opuntias are prickly pears (see prickly pear), composed of flat joints, stem segments arising one from the end of another. Opuntia occurs from the Peace River in western Canada almost to the tip of South America. In the Northern Hemisphere it is the most northern-ranging cactus. The most cold-hardy forms are small, some with joints only 2.55 cm (12 inches) long. In contrast, O. ficus-indica (or O. megacantha), the commonly cultivated prickly pear of Mexico, is treelike, reaching 5 m (16 feet), with a woody trunk and joints 3050 cm long or more.