Crassulacean acid metabolism in the Basellaceae (Caryophyllales)

C 4 and crassulacean acid metabolism (CAM) have evolved in the order Caryophyllales many times but neither C 4 nor CAM have been recorded for the Basellaceae, a small family in the CAM‐rich sub‐order Portulacineae. 24 h gas exchange and day–night changes in titratable acidity were measured in leaves of Anredera baselloides exposed to wet–dry–wet cycles. While net CO 2 uptake was restricted to the light period in well‐watered plants, net CO 2 fixation in the dark, accompanied by significant nocturnal increases in leaf acidity, developed in droughted plants. Plants reverted to solely C 3 photosynthesis upon rewatering. The reversible induction of nocturnal net CO 2 uptake by drought stress indicates that this species is able to exhibit CAM in a facultative manner. This is the first report of CAM in a member of the Basellaceae.