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In addition, areoles can produce spines of many different types to suit their needs. A typical areole may have one or a few long, sharp central spines, which serve as the primary defense. Beneath them are often numerous (10 or more) smaller, radial spines produced around the edge of the areole.
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Some of the
Opuntioideae have spines, as well as glochids, on their areoles; some have only glochids. Structurally, the glochids seem to be bristles rather than evolved leaves. They are detachable and resemble small, sharp splinters. Unlike the spines, glochids generally are barbed and are very
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Arakaki, Mónica; Christin, Pascal-Antoine; Nyffeler, Reto; Lendel, Anita; Eggli, Urs; Ogburn, R. Matthew; Spriggs, Elizabeth; Moore, Michael J. & Edwards, Erika J. (2011-05-17), "Contemporaneous and recent radiations of the world's major succulent plant lineages",
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For the cacti, areoles are an important evolutionary modification. They give rise to spines and glochids, which are their primary means of self-defense. In addition, because these spines arise from areoles and not directly from the
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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. Accordingly, the areoles distinguish the family
Cactaceae from other
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Areoles represent highly specialized branches on cacti. They evolved as abortive branch buds while their spines evolved as vestigial leaves. In branched cacti, such as
Opuntioidiae and the
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These may serve as a secondary defense against small creatures that can get past the central spines. In some species, though, such as
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appear to have been carried to parts of Asia and Africa, most likely by birds.
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This article is about the raised areas on cacti. For other uses, see
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Anderson, Edward F., The Cactus Family, Pub: Timber Press 2001
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Areoles contributed largely to the evolutionary success of the
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Bumps on cacti out of which grow clusters of spines
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