The distinctiveness of the cactus family shows itself not only in the flower structure, but also in one characteristic, that, although possessed by every cactus plant, is absent in all species of all other families. This is the spine cushion or areole. Whether or not spines are present, all cacti have areoles. Because these areoles differ in structure on different kinds of cacti, this is one way of distinguishing one cactus plant from another.