Scientists have uncovered how certain tropical trees evolved a special kind of photosynthesis called CAM (Crassulacean Acid Metabolism), which helps them survive in dry conditions. This process allows the trees to take in carbon dioxide at night, keeping their leaf pores closed during the day to prevent water loss. The study, led by Wolfram Weckwerth from the University of Vienna, examined the genomes of three species in the Clusia genus—Clusia rosea, Clusia minor, and Clusia major—to understand how repeated genetic changes over time contributed to the development of CAM. Their findings were recently published in the journal Nature Communications. The Clusia genus is unique because it includes the only known trees that use CAM. These species also display a wide range of photosynthetic strategies, from the standard C3 photosynthesis, where carbon dioxide is taken in during the day, to highly efficient CAM. The research revealed that all three species are polyploids, meaning their genomes were duplicated in the past. Over time, these expanded genomes underwent reorganization, leading to the evolution of different forms of CAM. The study showed that the development of CAM in Clusia was not the result of a single event but occurred through multiple rounds of genetic reorganization. For example, Clusia rosea uses a strong form of CAM, storing large amounts of carbon dioxide as malic acid at night. Clusia minor activates CAM only under stressful conditions, while Clusia major uses a combination of C3 photosynthesis and CAM. These differences in how the plants function were linked to variations in gene activity and metabolic processes identified by the researchers. The implications of this research extend beyond tropical trees. CAM plants require significantly less water than those using conventional photosynthesis, making them valuable models for improving crop resilience in dry climates. The newly available genomic data could help scientists identify the metabolic processes involved in efficient carbon dioxide absorption and water conservation. In the long term, this knowledge may aid in developing crops better suited to arid environments, helping agriculture adapt to climate change.