Euphorbia grandicornis "Cows Horn"
So what makes a plant a succulent? All plants store water, but succulent plants are specially adapted for it. Succulent plants are plants that retain water for long periods within special water holding tissues in leaves, stems or roots. They are usually adapted to hot dry climates but some epiphytic jungle plants are also succulent. They grow in the detritus that collects in the junctures of tree branches. Though rains are frequent, the material they root in dries quickly. Another important adaptation for succulents is found in leaf and stem shape. They are shaped so as to present the least amount of leaf or stem surface to the heat and dehydrating air. This slows the rate of water loss.
Leaf succulents usually have succulent stems as well, however some have stems that get rather woody over time and most of the water is retained by the leaves. Examples of leaf succulents are Crassulas, Aeoniums, and Sedums. Some leaf succulents such as Sansevieria, some Mesembs and certain Aloes and Agaves have no stems at all. While others may have succulent leaves, stems and roots.
Stem succulents include the Cacti, most Euphorbias and Stapeliads among others. Some stem succulents have no leaves at all and the process of photosythesis is taken over by the stems. Others may have tiny vestigial leaves and others non succulent leaves.
Some succulents don't have succulent leaves. They store water in an underground tuber, bulb or caudex and some a thickened trunk or roots. Usually the non succulent above ground growth dies off in winter and periods of drought. Some examples of this type of succulent are Adenium, Amorphophalus, Bowiea and Fockea among many others.
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