Updating the occurrence of crassulacean acid metabolism (CAM) in the genus Clusia through carbon isotope analysis of species from Colombia.

Clusia is a widely distributed neotropical genus with 321 currently described species. This remarkable genus is the only one known to contain trees sensu stricto with CAM photosynthesis. To survey the occurrence of CAM in Clusia species from Colombia, we determined the leaf stable carbon isotope composition (δ¹³C) of 568 specimens from 114 species deposited in 12 Colombian herbaria. In the vast majority of specimens, δ¹³C values indicated that C₃ photosynthesis was the principal contributor to carbon gain. δ¹³C values typical of strong CAM (less negative than -20‰) were observed in only five species, in four of them for the first time. All samples with CAM-type isotopic signatures were collected below 1,000 m a.s.l., whereas species with predominantly C₃ occurred from sea level to 3,500 m a.s.l. Together with information already available in the literature, we conclude that CAM is present in 22% (35/156) of the species of Clusia investigated thus far.