Cacti are succulent perennial plants. Cacti commonly have thick herbaceous or woody chlorophyll-containing stems. Cacti can be distinguished from different succulent vegetation by way of the presence of areoles, small cushionlike structures with trichomes (plant hairs) and, in almost all species, spines or barbed bristles (glochids). Areoles are changed branches, from which vegetation, greater branches, and leaves (while present) may also develop. In most species, leaves are absent, greatly decreased, or changed as spines, minimizing the amount of floor place from which water may be lost, and the stem has taken over the photosynthetic capabilities of the plant. Only the tropical genera Pereskia and Pereskopsis, both vines, have conventional-looking useful leaves, even as the leaves of the Andean Maihuenia are rounded, not flattened. The root structures are normally skinny, fibrous, and shallow, ranging broadly to take in superficial moisture.
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