Cacti are called all members of the family of angiosperm (Cactaceae). The family is very rich in genera and species (more than120 genera with over 2,400 species).
Visually, cacti are quite different from the other plants. This is due to the fact they are adapted to life in the desert and semi-desert regions and to the prolonged dry periods there.The leaves have evolved into spines, and besides the evaporation of less water through transpiration as compared to regular leaves, they protect the cactus plant from animals looking for water.Photosynthesis is carried out by the enlarged stems where water is stored.Unlike other succulent plants, the stem is the only part of core cactus where the process of photosynthesis is carried out. The flowers of the cacti most often spring from the so called areolae (from Latin - areola, diminutive of area — ‘open space’). They lack stems and stand on a calyx shaped pistil. Many of the species of cacti blossom at night as they are pollinated by night insects and bats. Some members of the Cacti family bear fruit and are used for food by humans.
The cacti are divided in two groups in terms of the conditions in which they live.One group grows in the tropical rain forests, while the other grows in the sandy and arid regions.
Cacti grow abundantly in the deserts and semi-deserts of North, South and Central America. Many cacti adapt themselves to other climates in other parts of the world with similar climate conditions, as they are brought there by man.