Coryphantha is a genus of the cactus family, Cactaceae, which contains about 45 species. Formerly, these species belonged to the genus Mammillaria, and some literature uses this genus name to refer to Coryphantha cacti. These cacti usually are native to the southwestern part of the U.S. and parts of northwestern Mexico. Generally, botanists identify the cacti by their long taproot and grooved tubercles. Many gardeners cultivate various species in this genus as house or garden plants.
Some other characteristics shared by most Coryphantha plants are that the flowers usually stem from the growing point of the plant and the cacti do not have leaves. Most of the cacti grow best when the temperature is above 40°F to 50°F (about 4.4°C to 10°C). Like most cacti plants, these plants thrive in full sun to light shade. Although many of the plants are global in shape, some may be cylindrical. Whether the Coryphantha cactus is clump-forming or solitary depends on the species and cultivar.
One of the Coryphantha species native to parts of Mexico is C. clava. This solitary growing cactus usually grows to a height of 12 inches (30 cm) with a diameter of 3 inches (7.5 cm). Its tubercles often are less than 1 inch (about 2 cm) across and have woolly axils. Generally, the diurnal flowers are yellow with contrasting brown outer segments and average about 1 inch (about 2.5 cm) long. The areoles produce one central spine that protrudes at a right angle from the plant and is surrounded by eight to 12 radials that lie almost flat to the plant.
The rhinoceros cactus, or C. cornifera, typically is native to parts of Hildago, Mexico, and mature plants often survive temperature drops to 25°F (about 4°C), although immature plants seldom survive temperatures below 50°F (about 10°C). The solitary-growing, cylindrical cacti may grow to 6 inches (15 cm) in diameter and 5 inches (12.7 cm) high. The short — under 1 inch (2.5 cm) long — central spine or spines are darker than the surrounding radial spines and sprout from non-woolly areoles.
The prickly beehive cactus, or C. echinus, is a solitary growing, global cactus that grows to a width and height of about 2 inches (about 5 cm). It usually sprouts three central spines that may measure up to 1 inch (2.5 cm) long with 16 to 30 shorter radial spines encircling them. All spines are grayish white, and the stem — the global part — is medium green. Usually the plant has 2-inch (5 cm) wide yellow flowers and green fruit.
A clump-forming cactus native to part of Mexico is the C. elephantidens, or elephant's tooth. Each of the globe-shaped heads is about 6 inches (15 cm) in diameter with round tubercles about 1.5 to 2.5 inches (3.8 to 6 cm) wide. The white woolly axils have no central spines but sport six to eight reddish-brown to brown radial spines that fade to light gray near the areole.
Two other Coryphantha cacti are the long mamma, or C. macromeris, and the Santa Cruz beehive, or C. recurvata. Long mamma is a clumping type of cactus that is native to parts of New Mexico and Texas in the United States and part of Mexico. Santa Cruz beehive is native to the U.S. in southern Arizona and parts of Mexico. Both of these cacti have masses of spines that almost obscure the stem. Long mamma's flowers usually are pinkish purple to light pink, but the Santa Cruz beehive's flowers tend to be greenish yellow.