A desert plant, the cactus grows in dry areas where other types of plants have trouble surviving. Its ability to hold water keeps it alive, and its sharp spines discourage animals from eating it. The cactus belongs to the family of plants called Cactaceae. Where cacti grow - A type of cactus known as the Engelmann prickly pear commonly grows in the southwestern United …
Scientists who study plants estimate that there are about 1,650 species (types) of cacti. These plants grow mainly in the dry regions of the southwestern United States, Mexico, Central America, and southern South America. Mexico has the greatest number and variety of cacti. Members of the tropical genus Rhipsalis can be found in East Africa, Madagascar, and Sri Lanka. Scientists, however, think that the cacti were brought to those regions from elsewhere. Most cacti grow in the ground. Some cacti, known as epiphytes, grow on other plants; others may grow on hard substances such as rocks. How cacti surviveMost types of cacti are well-adapted to dry regions. The cactus is a succulent plant, meaning that it has fleshy, thick tissues that are able to take up and hold large quantities of water. This stored water lets the cactus survive during dry periods. Unlike many plants that have deep roots, the cactus has roots that spread out near the surface of the soil. This difference is important to the survival of the cactus because it enables the plant to absorb water from a wide area during the few times the desert gets rain. Physical features - Although there are several different varieties of barrel cactus, in general they have strong stiff …
Cacti are known for their sharp spines. These come from small cushionlike tissues called areoles that dot the surface of the plant in patterns. The flowers, branches, and leaves of cacti, when present, also arise from areoles. (Most cacti do not have leaves. Cacti that do have leaves have very small ones that drop off as the plant grows.) Some cacti produce large, colorful flowers. The stem surface largely determines the appearance of the plant. The surface can be smooth or covered with outgrowths. Epiphyte cacti tend to have thin, flattened stems. Some cacti are in the form of very spiny globes. Cacti vary greatly in size. The cactus called the prickly pear grows in low bunches, while the giant cactus known as the saguaro can be 50 feet (15 meters) tall with column-like stems and branches up to 2 feet (about 0.6 meter) thick. Uses for cactiCacti are often grown for decorative purposes. Many unusual and beautiful varieties are prized as houseplants. In South America some species are used as fences to define boundaries. Arizona has adopted the saguaro as its state flower. The Saguaro National Monument in the state preserves this cactus. Among the most beautiful cacti is the night-blooming cereus. Its blossoms open in a single night but wither when sunlight appears. Species such as the chollas are cultivated as food. The egg-shaped fruit of the saguaro is edible. Barrel cacti can be used as a source of water in times of scarcity. The prickly pear bears a pear-shaped fruit that can be eaten. Its fruit also contains a relatively large amount of water. Some cacti, such as peyote, contain a mind-altering drug called mescaline that has been used in folk medicine. |