cactus

Cactus is the ancient Greek name for a prickly plant, now applied as a general term to many different succulent and prickly plants. They vary in shape and size and have no leaves, photosynthesis occurring in green stems. The lack of leaves is an adaptation for conserving water, as is the common spherical shape.

Cacti are adapted for desert life in a number of ways. They have fleshy tissue in which to store water and their leaves are reduced to spines to lessen water loss by transpiration. Cactus roots are branching and shallow, adapted to gathering surface water from a large area.

The rugged beauty of the desert areas of Arizona, with their spectacular rock formations, draws millions of visitors every year. Famous for their wide variety of vegetation, particularly cacti, these deserts have plants found nowhere else in the USA.

Prickly pear plant, southern Mexico. The name refers to the edible fruit of some species of cactus, which are an important food source in many tropical and subtropical areas. The prickly pear is grown as a forage crop, as well as for its fruit, and its seeds are used to produce oil. The water-storing flat stems (particularly of spineless varieties) are also used to feed stock during times of severe drought.

Cacti in southern Mexico. Cacti belong to the New World Cactaceae family and are specially adapted to living in arid conditions.

Star cactus (Astrophytum ornatum), also known as bishop's cap cactus. The star cactus is one of four species of spherical, spiny cactus plants that comprise the genus Astrophytum. During the summer the star cactus produces numerous large, daisylike yellow flowers. Astrophytum can grow up to 4 m/13 ft in diameter. It is native to Mexico.

Strictly, any plant of the family Cactaceae, although the word is commonly used to describe many different succulent and prickly plants. True cacti have a woody axis (central core) surrounded by a large fleshy stem, which takes various forms and is usually covered with spines (actually reduced leaves). They are all specially adapted to growing in dry areas.

Cactus flowers are often large and brightly coloured; the fruit is fleshy and often edible, as in the case of the prickly pear. The Cactaceae are a New World family and include the treelike saguaro and the night-blooming cereus with blossoms 30 cm/12 in across.