Abstract
Succulent plants inhabiting desert depressions in eastern Arabia were predominantly leaf succulents exhibiting a variety of adaptations important for survival in extreme aridity. These adaptations included investing a high proportion of carbon gain into making succulent leaves with low stomatal densities. Succulents exhibiting C3photosynthesis with a requirement for widely open stomata were arido-passive plants that avoided water stress by initiating precocious flowering long before the onset of the dry season. Succulents exhibiting C4photosynthesis and C3–CAM intermediates with high water-use efficiency benefited from more resources by being able to extend their growth into the dry season. Arido-active succulents survived the dry season by undergoing an extensive leaf loss accompanied by midday stomatal closure, or by undergoing a C4–CAM shift aimed at conservation of water. Various indices commonly used for assessing succulence have also been compared.