succulent, any plant with thick fleshy tissues adapted to water storage. Some succulents (e.g., cacti) store water only in the stem and have no leaves or very small leaves, whereas others (e.g., agaves) store water mainly in the leaves. Most succulents have deep or broad root systems and are native to either deserts or regions that have a semiarid season. Succulent plants are found in more than 60 plant families, with members of Aizoaceae, Cactaceae, and Crassulaceae being dominantly succulent. A number are cultivated as ornamentals and houseplants, including Aloe, Echeveria, Kalanchoe, and others.

One common adaptation in many succulents is the timing of the opening of their stomata, which are small mouthlike structures on the surface of plant leaves and stems. Stomata allow for the uptake of carbon dioxide from the environment and the loss of water and oxygen to the environment. Unlike those of most plants, the stomata of many succulent plants are closed during the day and open at night. As a result, the loss of water (transpiration) during the hot dry daytime hours is minimized and carbon dioxide (CO₂) uptake occurs in the dark. These succulent plants, therefore, exhibit a modified form of CO₂ fixation and photosynthesis called crassulacean acid metabolism.