Areolas . They are small structures with a normally plush appearance, which are along the ribs or on the tubers of numerous globose species.
Summary
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- 1 Location
- 2 Adaptation
- 3 Importance
- 4 Sources
Location
Areolas are curious organs that characterize cacti . In the same way that the buds of trees and other plants, they give rise to leaves, buds and flowers, but they also originate hairs, bristles, glochids and thorns. They are shaped like small pads, sometimes pubescent, and can be located along the ribs (columnar cactus and some globular) or on the tuber (several globular species). In the areolas there are two vegetation points: one that generates flowers and buds, and another that gives rise to thorns. They can be found together in the same areola (Cereus, Echinopsis, Opuntia) or separately, one on the tuber, place of growth of spines, and the other displaced towards the axilla of the same, point where the flowers and shoots are produced (Mammillaria, Coryphantha).
They are growth points equivalent to the buds of other plants, which will give rise, for example, to other organs, such as flowers and thorns.
The areola is the distinctive feature of the cactaceae family and serves to identify it as a separate family from succulent plants.
The areolas give rise to the spines or, in certain cacti, to small detachable glochids that constitute an extra form of protection. They are clearly visible and generally appear as small bumps of light or dark colors, from which the groups of spines arise.
Adaptation
The areolas represent highly specialized branches. It is believed that they evolved to adapt to the arid desert climate, being reduced to simple buds from which rudimentary leaves emerged that, over time, became spines to protect plants from predation and reduce water loss.
Some cacti lack spines on their areoles but instead have glochids, which resemble small cushions with short, sharp hairs that are very difficult to remove when pricked into the skin.
Importance
Areolas represent an important evolutionary modification for these plants. They give rise to thorns, which are their main means of self-defense and, in addition, the fact that these thorns arise from them instead of directly from the stem provides a much more effective coating than in other plants.
They produce thorns of very different size, number and type to adapt to the specific needs of each species. A typical areola may have one or more long, sharp central spines, which serve as a defense. Beneath them are often numerous (10 or more) smaller radial spines that emerge around the edges and serve to shade the plant and retain some fresh air between them and the stem .
