Are there species in the genus Clusia with obligate C₃ photosynthesis?

Most of the species in the genus Clusia are very flexible in their photosynthetic pathway, and are C₃-photosynthesis/Crassulacean acid metabolism (CAM) intermediate species; therefore, the identification and dear assignment of Clusia-species to C₃- or CAM-pathways is difficult. We made an attempt to characterize obligate C₃-photosynthesis species within that genus. Therefore, we selected five species of the family Clusiacea (four of the genus Clusia and one of the genus Oedematopus) on the basis of their low leaf succulence as potential obligate C₃-photosynthesis species. All of them showed a C₃-photosynthesis pattern of gas exchange under well-watered conditions and their δ¹³C-values were also found to be in the range of obligate C₃-photosynthesis plants. Under drought stress two of them (C articulata and C. cruiva) proved to be C₃-photosynthesis/CAM intermediate species, while C. parviflora, C. multiflora and most likely O. mirandensis did not show any nocturnal CO₂-fixation. However, in C. parviflora and O. mirandensis some nighttime accumulation of malate by internal CO₂-recycling might occur. So far, C. multiflora seems to be the only known Clusia species with neither nocturnal net CO₂-uptake nor malate accumulation.