Cactus

A cactus (plural cacti, cactuses, or cactus) is any member of the flowering plant family Cactaceae, a group of roughly 120–130 genera and between about 1,400 and 1,900 known species of succulent, typically spiny plants native almost exclusively to the Americas. Cacti are distinguished from all other flowering plants by the areole, a specialized cushion-like structure from which spines, flowers, and new branches emerge. Renowned for their ability to survive in some of the driest environments on Earth, cacti combine water-storing tissues, reduced or absent leaves, and a special form of photosynthesis that minimizes water loss. Beyond their ecological importance in deserts and dry forests, cacti have long served humans as food, dye, medicine, ceremonial plants, and ornamentals, and they occupy a prominent place in the cultures of the Americas, particularly Mexico.

Description and Morphology

Despite enormous variation in size and habit, cacti share a common body plan. The stem is the principal organ of photosynthesis and water storage; it is typically fleshy, ribbed or tuberculate, and covered by a thick, waxy cuticle. The ribs allow the stem to expand after rainfall and contract during drought, while folds of tissue shade parts of the surface from intense sunlight. Leaves are absent or reduced to scales in nearly all species; in cacti the spines themselves are modified leaves. In the genus Pereskia, considered among the most "primitive"