any of about 50 species of the genus Gymnocalycium, family Cactaceae, native to South America and named for the chinlike protuberance below each spine-bearing areole (special bud) on the ribs. Many natural and cultivated varieties are available, the most outstanding of which is G. mihanovichii Hibotan, a glowing red, which must be grown grafted onto a normal cactus because it lacks chlorophyll and cannot synthesize its own food. Varieties of other colours also have been developed and are seen in the florist trade.