The Occurrence and Phylogenetics of Crassulacean Acid Metabolism in the Portulacaceae

Abstract

The plant family Portulacaceae is a relatively small family (∼19 genera and ∼425 species) with a widespread distribution. Species of the Portulacaceae range in size from small herbaceous plants to shrubs that measure up to 4 m in height. Most members of the family have leaves that range from fleshy to fully succulent and live in very diverse habitats ranging from shady understory plants to plants exposed to full sunlight. The Portulacaceae have members that utilize different photosynthetic pathways ranging from C3 to C4 to Crassulacean acid metabolism (CAM) to CAM‐cycling plants. We are interested in the prevalence of the CAM photosynthetic pathway in this family. We studied the nocturnal CO2 uptake, diurnal acid fluctuation, and phosphoenolpyruvate (PEP) carboxylase activity of different members of the Portulacaceae. Our results indicate the highest levels of CAM activity in the genera of Anacampseros, Portulacaria, Ceraria, and Talinopsis. Intermediate in their CAM activity were the genera Talinum, Port...