cactus, any plant of the family Cactaceae, a large group of succulents found almost entirely in the New World. A cactus plant is conspicuous for its fleshy green stem, which performs the functions of leaves (commonly insignificant or absent), and for the spines (not always present) of various colors, shapes, and arrangements. Cactus flowers are notably delicate in appearance although usually large and showy; they are commonly yellow, white, or shades of red and purple. Many species are pollinated by bats. Cactus fruits are berries and are usually edible. A cactus plant appears on the coat of arms of Mexico, and the blossom of the giant cactus, or saguaro ( Cereus giganteus ), is the state flower of Arizona.