Mok, D. W. L.; VanBuren, R.; Gilbert, K. J.

Premise Pinguicula are carnivorous plants occupying a wide range of habitats, from wetlands to barren rock cliffs, where CAM photosynthesis was recently discovered in several species. This ecological and physiological diversity makes the genus a promising system for exploring the environmental drivers and evolutionary transitions underlying variation in CAM. Here, we present a physiological survey of CAM with a particular focus on the Mexican Clade, which contains the recently identified CAM species. Methods We conducted a carbon isotope survey of live and herbarium specimens to identify candidate CAM species. We then measured diurnal gas-exchange patterns and changes in leaf titratable acidity to quantify CAM activity. Results Pinguicula species exhibited a variety of photosynthetic phenotypes. Pinguicula vulgaris showed no detectable evidence of CAM, whereas P. cyclosecta and P. moranensis demonstrated a C3-CAM physiology with most net assimilation via C3. Pinguicula martinezii also showed the same C3-CAM physiology under well-watered conditions but had strong facultative induction of CAM with drought. Pinguicula agnata displayed net assimilation via CAM. Titratable acidity had a positive correlation with {delta}13C within the species we sampled. Conclusions Our results support the existence of a CAM physiological continuum within Pinguicula. Notably, closely related species encompass physiologies that span the large variation of CAM. This diversity provides a rare opportunity for future studies to investigate the evolution of CAM in closely related species, including differences and similarities between differing states across the continuum.