Areole

In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines.

Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants.

The areole was one of the unique features that cacti developed, possibly in adaptation to the ambient climate in the area in which they emerged.

In some species, though, such as Cephalocereus senilis, the tangle of hairy radial spines serves to shade the plant and retain a layer of cool, humid air next to it.

Areoles contributed largely to the evolutionary success of the Cactaceae throughout the range of the family, and account for the diversification seen in the many species today.