Publication Date

January 2021


Honorable Mention

Class Year



Ecology and Evolutionary Biology


Erika Edwards


With at least a hundred independent origins among land plants, the CAM and C4 photosynthetic pathways represent one of the most notable examples of global convergent evolution of a complex trait. While biochemically similar, CAM and C4 are generally understood to be two distinct ecological adaptations evolving along separate trajectories. However, the purslanes (Portulaca), a globally widespread clade of around 100 species of annual and perennial succulents, are able to operate both CAM and C4 cycles in the same leaf. Portulaca likely originated from a facultative CAM ancestor and then evolved a C4 system at least three times while maintaining its CAM capabilities. Here, we use a dataset of 55,000 specimen records curated from the Global Biodiversity Information Facility (GBIF) and the Australian Virtual Herbarium, combined with high-resolution environmental rasters, to investigate the climate niche of Portulaca. In comparison to its closest relatives (Anacampserotaceae, Talinaceae, Cactaceae, and Calandrinia)—which include facultative and constitutive CAM plants but no C4 plants—Portulaca is able to persist in areas experiencing much higher temperatures and precipitation levels. Ancestral character state reconstructions conducted on the best-supported phylogenies for Portulaca and Anacampserotaceae allow us to infer the ecological consequences of evolving the C4+CAM pathway as opposed to C3+CAM or strong CAM. Further research into Portulaca’s anomalous photosynthetic system will dramatically improve our understanding of which environmental selective pressures have driven land plants to repeatedly evolve CAM and C4 and how this diverse and ecologically important group of plants may respond to future climate change.

Open Access

This Article is Open Access