Editing Cactus (section)

===Areoles===

{{multiple image
| title             = Cactus areoles
| total_width       = 400
| perrow            = 2 / 3
| image1            = Pereskia grandifolia areole.jpg
| caption1          = Areole of ''[[Rhodocactus grandifolius]]'' showing its position relative to leaves
| image2            = Cut Cereus (brightened).jpg
| caption2          = Cross-section of ''[[Cereus (plant)|Cereus]]'' showing areoles with spines and wool
| image3            = Echinopsis candicans (3).jpg
| caption3          = Areoles of an ''[[Echinopsis]]'' species
| image4            = Astrophytum capricorne areole.jpg
| caption4          = Close-up of an areole of ''[[Astrophytum capricorne]]'' showing fine wool
| image5            = Cactus 4a - geograph.org.uk - 1446436 cleaned.jpg
| caption5          = Flowers appear from the upper part of an areole, spines from the lower (''Cereus'' species).
}}

[[Areole]]s are structures unique to cacti. Although variable, they typically appear as woolly or hairy areas on the stems from which spines emerge. Flowers are also produced from areoles. In the genus ''[[Leuenbergeria]]'', believed similar to the ancestor of all cacti, the areoles occur in the axils of leaves (i.e. in the angle between the leaf stalk and the stem).{{sfnp|ps=none|Anderson|2001|p=566}} In leafless cacti, areoles are often borne on raised areas on the stem where leaf bases would have been.

Areoles are highly specialized and very condensed shoots or branches. In a normal shoot, [[Plant stem|nodes]] bearing leaves or flowers would be separated by lengths of stem (internodes). In an areole, the nodes are so close together, they form a single structure. The areole may be circular, elongated into an oval shape, or even separated into two parts; the two parts may be visibly connected in some way (e.g. by a groove in the stem) or appear entirely separate (a dimorphic areole). The part nearer the top of the stem then produces flowers, the other part spines. Areoles often have multicellular hairs ([[trichome]]s) that give the areole a hairy or woolly appearance, sometimes of a distinct color such as yellow or brown.{{sfnp|ps=none|Anderson|2001|pp=15–37}}

In most cacti, the areoles produce new spines or flowers only for a few years and then become inactive. This results in a relatively fixed number of spines, with flowers being produced only from the ends of stems, which are still growing and forming new areoles. In ''Pereskia'',  a genus close to the ancestor of cacti, areoles remain active for much longer; this is also the case in ''[[Opuntia]]'' and ''[[Neoraimondia]]''.{{sfnp|ps=none|Anderson|2001|pp=15–37}}