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cactus, any plant of the family Cactaceae, a large group of succulents found almost entirely in the New World. A cactus plant is conspicuous for its fleshy green stem, which performs the functions of leaves (commonly insignificant or absent), and for the spines (not always present) of various colors, shapes, and arrangements. Cactus flowers are notably delicate in appearance although usually large and showy; they are commonly yellow, white, or shades of red and purple. Many species are pollinated by bats. Cactus fruits are berries and are usually edible. A cactus plant appears on the coat of arms of Mexico, and the blossom of the giant cactus, or saguaro (Cereus giganteus), is the state flower of Arizona.
The plants vary from small, round globes to epiphytes, vines, and large treelike forms. The reduced leaf surface, the enlarged fleshy stem, which is well fitted to store water and to retain it, and the ramified and extensive root system (much reduced in cultivated cacti) make the plant particularly adapted to regions of high temperature and long dry periods. Cacti are not restricted to desert regions, however, for in America they range from the tropics into Canada.
Most cacti bloom in the spring for a very short period, sometimes for only a few hours. The blossoms are noticeably sensitive to light, and often different species blossom only at specific times of the day. One of the most famous of the cacti is the night-blooming cereus usually classified as Selenicereus or C. grandiflora (several other night-blooming cactus species bear the same common name). Its fragrant blossoms unfold at a visible rate after sunset and last only a single night. In many of its native habitats the flowering of this cactus is celebrated with festivals.
The largest cactus genus is Opuntia, jointed-stemmed species recognizable by the fleshy stems made up of either cylindrical (in the cane cacti and the chollas) or flattened (in the prickly pears) joints called pads. The large pear-shaped berries of several of these species are edible, e.g., the cultivated varieties of the Indian fig and the tuna. This fruit is common in Mexican markets; the plants have been widely naturalized in the Mediterranean countries, Australia, and elsewhere as a source of food. Some species are used as livestock feed. Most opuntias grow so rapidly to a large and ungainly size that they are unsuitable for cultivation as ornamentals, and in the wild often become weeds. Dragon fruit or pithaya, from species of Selenicereus (also classified as Hylocereus), are also economically important.
However, the major economic importance of the cactus family is in the horticultural trade. Among those cultivated for their showy blossoms are the Christmas cactus (Zygocactus) and species of Echinocereus and of Epiphyllum, the orchid cactus. The pincushion cacti (Mammillaria), the golden ball cactus (Echinocactus), and the hedgehog cactus (Echinopsis) are among the many grown as oddities for their curious appearance.
The cochineal nopal cactus (Nopalea cochenillifera, also classified as Opuntia cochenillifera) is traditionally cultivated as a host for the cochineal insect, and the hallucinatory drug mescaline occurs in the genera Lophophora (peyote) and Trichocereus. Other cacti are used as a substitute for wood, as stock feed, and for hedges.
See L. Benson, The Cacti of the United States and Canada (1982) and A. C. Gibson and P. S. Nobel, The Cactus Primer (1986).
(Cactaceae), a family of dicotyledonous perennial plants usually having thickened, succulent, fleshy stems covered with spines, hairs, or bristles. Cacti may be treelike, shrubby, or vinelike; some, such as those of Pereskioideae are small trees. The stem may be spherical, ovoid, cylindrical, columnar, or occasionally flattened and segmented. As a rule, the stem does not have developed leaves (normally developed leaves are found only in the subfamily Pereskioideae), but it is adapted for photosynthesis and transpiration, as well as for the accumulation of moisture. The cactus stem has a well-developed water-bearing parenchyma (large cacti can hold up to 2, 000 liters of water), and the cells contain a mucous substance that impedes the loss of water. Many cacti have a waxy surface or a thick, sometimes woolly, covering. There are a few stomata below the surface, and almost all cacti have ribs or papillae (modified leaf bases). Cacti are distinguished by the presence on the stems of areoles, clearly defined areas with hair and a spine originating from the axillary buds and their scales.
The flowers are often large, sometimes with diameters of up to 25 cm, brightly colored, usually solitary (occasionally arranged in apical inflorescences), almost always bisexual, and usually regular. The perianth has many spirally arranged segments, the outermost of which are the sepals and the innermost, the staminal petals. In many genera the petals are fused at the base into a tube. There are many stamens, and the ovary is usually inferior. The fruit is usually polyspermous, fleshy, berrylike, and sometimes dry. Many cacti blossom only late in the evening or at night. They are pollinated by insects or birds (including hummingbirds), although sometimes by bats. The seedlings of many cacti have seed leaves.
There are about 85 genera (according to other sources 50-220), comprising more than 2, 000 species, found almost exclusively in North and South America. Half of all the species are found in Mexico. Only one genus, Rhipsalis, occurs in tropical Africa (probably imported), on Madagascar and the Mascarene Islands, and in Sri Lanka. Cacti usually grow in tropical and subtropical deserts, extending in some areas up to 4, 500 m into the mountains; they are rarely found in tropical rain forests, in savannas, or along seacoasts. Some cacti, such as various species of Opuntia, are naturalized in Australia, China, the Mediterranean region, and other countries; in the USSR they grow on the Southern Crimean Shore.
Cacti are used for food (the fruit and the flesh of the stems), fodder (particularly the spineless members of Opuntia), fuel, light building material (the woody stems of some species), and the making of hedgerows (especially prickly Opuntia and some members of the genus Cereus). Many cactus species are grown indoors and in greenhouses (Mammillaria, Opuntia, Cereus, Cephalocereus, and Epiphyllum). Cacti are propagated by seeds, cuttings, or graftings. Depending on the species, the seeds may retain their germinating potential for several years. The sprouts appear between three and 30 days after sowing. Grafting is done from May to August. For many cactus species, Trichocereus Spachianus, Trichocereus pachanoi, Eriocereus Jusberta, and Pe-reskia aculeata are used as stock.
Cacti are grown in a soil mixture composed of leaf mold, clay sod, large-grain sand (with an admixture of gravel), crushed charcoal, and lime, with the proportion depending on the species. Organic fertilizers are used only for epiphytes, such as Zygocactus and Epiphyllum; mineral fertilizers are used for others.
Cacti blossom from early spring to late autumn; species of Zygocactus and Rhipsalis flower in winter. When they are not flowering, most species are dormant. In winter most cacti grown indoors and in greenhouses are kept at a temperature of 8°-10°C, although some are maintained at 5°-6°C and epiphytes at 14°-16°C; they are watered infrequently. In summer cacti require a warm, sunny spot, fresh air, much watering, and regular spraying. During the budding period, some cacti should not be moved, as this may cause the buds to fall.
REFERENCESD’iakonov, V. M., and N. I. Kurnakov. Kaktusy i ikh kul’tura v komnatnykh usloviiakh. Leningrad, 1953.
Pazout, F., Z. Valnicek, and R. Subik. Kaktusy. Prague, 1963. (Translated from Czech).
Takhtadzhian, A. L. Sistema i filogeniia tsvetkovykh rastenii. Moscow-Leningrad, 1966.
Backeberg, C. Die Cactaceae, vols. 1-6. Jena, 1958-62.
Backeberg, C. Das Kakteenlexikon. Jena, 1966.
R. A. UDALOVA and S. G. SAAKOV