areole

1. A sunken cushion representing a condensed lateral shoot from which spines, branches, and flowers arise in cacti. Areoles may occur either singly on tubercles (e.g. in Mammillaria zeilmanni-ana) or in rows along raised ridges.

2. Any area outlined on a surface, e.g. a segment of leaf lamina surrounded by veins. A surface divided into areoles, e.g. lichen thalli split by cracks into roughly hexagonal areas, is described as areolate.