Barrel cactus is the common name for the cactus species of the genus Ferocactus. The name sometimes also refers to members of the closely related Echinocactus genus. There are from 25 to 30 species of barrel cactus belonging to the Ferocactus genus and six species in the Echinocactus genus. The two groups have much the same growth habits and appearance, and both are found in the southwestern U.S. and in Mexico.
Cacti in these groups generally share the stereotypical barrel shape, though some are round or grow in clumps. They range in height from less than 1 foot (about 30 cm) to 12 feet (about 3.5 meters) and most have a pleated surface. Barrel cacti are known for their formidable spines, which range in length from 2 inches to 10 inches (about 5 cm to 25 cm). The spines, which can be straight or hooked, are white, yellow, brown or a brilliant red.
Barrel cactus flowers are stiff and funnel-shaped. The flowers, which grow from the top of the cactus, come in varying shades of white, yellow, red and purple. Many have a darker stripe down the center of their petals. Bees are the usual pollinator.
The fruits cluster at the top of the plant where the flowers grew. Most barrel cactus fruits are yellow and tube-shaped. Ferocactus fruits have a moist rind, while the rind of the Echinocactus fruit is dry. All fruits have densely packed seeds in a dry interior. Bighorn sheep, javelina, birds, rodents and deer eat the flowers and fruit of the barrel cactus, while the plants themselves are food for javelina, jackrabbits, cactus beetles and pack rats.
A true desert environment — the kind where barrel cacti are found — has minimal rainfall, quickly draining soil, very hot days and cool to cold nights. As ornamental plants they do well in USDA zones 9 through 11 with low water, good drainage and full sun. Most species will endure occasional frost. Some species live as long as 130 years, but most do not reach 100 years old.
It is commonly believed that the barrel shape of these plants indicates a reservoir of water inside that can be easily tapped by travelers, but this is not accurate. There is water in the pulp of the interior, but it is not easily extracted and is often very alkaline. Animals and those skilled at living off the land may obtain useful moisture from the plants but, in general, they are not a good source of emergency water.