Forty years of research into Crassulacean Acid Metabolism in the genus Clusia : anatomy, ecophysiology and evolution.

Clusia is the only genus containing dicotyledonous trees with a capacity to perform Crassulacean acid metabolism (CAM). Since the discovery of CAM in Clusia, 40 years ago, several studies have highlighted the extraordinary plasticity and diversity of life forms, morphology, and photosynthetic physiology of this genus. In this review we revisit aspects of CAM photosynthesis in Clusia and hypothesize about the timing, the environmental conditions and potential anatomical characteristics that led to the evolution of CAM in the group. We discuss the role of physiological plasticity in influencing species distribution and ecological amplitude in the group. We also explore patterns of allometry of leaf anatomical traits and their correlations with CAM activity. Finally, we identify opportunities for further research of CAM in Clusia, such as the role of elevated nocturnal accumulation of citric acid, and gene expression in C3-CAM intermediate phenotypes.