A cactus (plural cacti, cactuses, or less commonly, cactus) may be a member of the family Cactaceae,] a family comprising about 127 genera with some 1750 known species of the Caryophyllales . The word “cactus” derives, through Latin, from the traditional Greek κάκτος, kaktos, a reputation originally employed by Theophrastus for a spiny plant whose identity is not certain. Cacti occur during a wide selection of shapes and sizes. Most cacti sleep in habitats subject to a minimum of some drought. Many sleep in extremely dry environments, even being found within the Atacama Desert , one among the driest places on earth. Cacti show many adaptations to conserve water. most cacti are succulents, meaning they need thickened, fleshy parts adapted to store water.