Cactus, the common name for a family of desert plants. The plural is cacti or cactuses. Most species bear sharp, needlelike spines, which protect the plants from foraging desert animals. Cacti are famed for their ability to resist drought, which they owe to the fact that moisture from inside the plant evaporates very slowly through the plant's skin.

Cacti grow in hundreds of different shapes. The fibrous, juicy stems may be globular, cylindrical, branched, trailing and vinelike, ribbed, grooved, or knob-bearing. Only two species have true leaves. The rest of the 2,000 species are leafless.

The bunny ears cactusThe bunny ears cactus bears sharp spines on its velvety green stems.
Kinds and Uses of Cactus

Since 1900, cactus-growing has become a popular hobby. Most of the smaller species and the young forms of larger cacti are easily grown in the home. Among these are living-rock, star cactus, pincushion cactus, chilotes, hedgehog cactus, and melon cactus.

One of the most useful cacti is the prickly pear, which was introduced into the Mediterranean region and elsewhere. The fruit, about the size of a hen's egg, is soft and rather sticky but has a pleasant taste. Spineless types are sometimes fed to livestock. In Mexico, the dried plants are used as fuel. The Indian fig is a species noted for its juicy fruit. Some prickly-pear cacti are also known as tuna, others as cholla.

A treelike cactus called the cochineal plant was once the most important economic species. It is the chief food of the cochineal insect, from which a scarlet dye is produced. For some uses cochineal dye has largely been replaced by synthetic dyes. The cactus is now grown mainly for ornament.

There are over 30 species of night-blooming cereus, climbing cacti with large, white flowers. The plants are grown outdoors in the South and as houseplants in colder climates.

The giant saguaro cactus reaches a height of 60 feet (18 m). It grows in Arizona, New Mexico, and California. The blossom is the state flower of Arizona. A distinctive stand of these huge plants, near Tucson, is preserved as Saguaro National Monument. The organ-pipe cactus is another large species, found in Arizona and Mexico. Organ Pipe Cactus National Monument was established in 1937 near Ajo, Arizona.

The peyote has a buttonlike crown that yields mescaline, a hallucinogen. Several other cacti yield substances used in medicine.

A spineless Brazilian species, known as the crab, or Christmas, cactus, is a popular houseplant. It requires more water than other cacti, and is a branched plant with leaflike stems. This cactus is frequently grown in hanging baskets and blooms around Christmastime. The red flowers are 2 ½ to 3 inches (6.4 to 7.6 cm) across.

One of the easiest cacti to grow is the rat-tail cactus with its thin, ribbed stems. A popular window plant, it has crimson flowers and bristling red fruit.

In some tropical regions cacti are used as a living fence to pen in small livestock. The tender shoots of one species are eaten raw as a salad, and are also cooked as a vegetable. Some species have long, woody stems that are used in building or to make ornamental walking sticks. Luther Burbank produced a number of varieties of spineless cactus suitable for forage in arid lands. The hairbrush cactus, a species with burlike fruits, was used by the Indians of the Southwest to make combs.

Indoor Growing

Cacti need plenty of fresh air and a dry atmosphere. Heat is not as important as dryness, but the temperature should be between 50 and 75 F. (10 and 24 C.) for best growth. Cacti will quickly rot if watered too much. In winter, especially, they need water only once a week. At other times, they should be watered not more than three times a week.

A suitable soil for most indoor cacti is composed of two parts sand, two parts loam, and one part crushed soft brick or potsherds. Bone meal and ground limestone may be added to the soil.

Cacti make up the family Cactaceae. Living-rock is Ariocarpus fissuratus; star cacti belong to the genus Astrophytum; pincushion cacti belong to the genera Coryphantha and Mammillaria. Chilotes is Epithelantha micromeris; hedgehog cactus is Echinocactus grusoni; melon cacti make up the genus Melocactus.

The many species of prickly-pear cacti make up the genus Opuntia; Indian fig is O. ficus-indica. The cochineal plant is Nopalea cochenillifera. Night-blooming cereus belong to the genera Selenicereus, Nyctocerem, and Hylocereus. Giant saguaro cactus is Carnegiea gigantea. Peyote is Lophophora williamsi. The Christmas cactus is Zygocactus truncatus. Organ-pipe cactus is Pachycereus marginatus; hairbrush cactus is P. pectenaboriginum.