Crassulacean

Crassulacean refers to Crassulacean acid metabolism (CAM), a photosynthetic pathway used by many plants to survive in water-limited environments. Although CAM is named for the Crassulaceae family, it is widely distributed across plant groups, including Cactaceae, Bromeliaceae, Orchidaceae, and Aizoaceae.

During the night, CAM plants open their stomata to take in carbon dioxide. The CO2 is fixed by the enzyme phosphoenolpyruvate carboxylase into four-carbon compounds such as oxaloacetate, which is reduced to malate and stored in vacuoles as malic acid. In the daytime, when stomata are closed to conserve water, malic acid is decarboxified to release CO2 for the Calvin cycle, allowing photosynthesis to proceed with minimal water loss.

CAM enhances water-use efficiency and is common in arid and semiarid habitats, hot deserts, and rocky outcrops. Some plants exhibit facultative CAM, switching between CAM and C3 depending on environmental conditions; others show obligatory CAM. CAM is often discussed in terms of variants or strategies such as CAM cycling and CAM idling, which describe different patterns of carbon gain and retention under stress.

Examples include many succulent ornamentals in Crassulaceae, such as Crassula and Sedum, and commercially important crops like pineapple (Ananas comosus). CAM’s ecological and physiological features make it a focus of study for drought tolerance and carbon economy in plants.