biostudies-literatureSage RFNatural Sciences and Engineering Research Council of Canada DiscoveryNational Science Foundation753-770https://www.ebi.ac.uk/biostudies/studies/S-EPMC10799994biostudies-literatureUnknown132(4)<h4>Background and aims</h4>CAM photosynthesis is hypothesized to have evolved in atmospheres of low CO2 concentration in recent geological time because of its ability to concentrate CO2 around Rubisco and boost water use efficiency relative to C3 photosynthesis. We assess this hypothesis by compiling estimates of when CAM clades arose using phylogenetic chronograms for 73 CAM clades. We further consider evidence of how atmospheric CO2 affects CAM relative to C3 photosynthesis.<h4>Results</h4>Where CAM origins can be inferred, strong CAM is estimated to have appeared in the past 30 million years in 46 of 48 examined clades, after atmospheric CO2 had declined from high (near 800 ppm) to lower (<450 ppm) values. In turn, 21 of 25 clades containing CAM species (but where CAM origins are less Annals of botanyAtmospheric CO2 decline and the timing of CAM plant evolution.PMC10799994IOS-1754662RGPIN-2017-06476Edwards EJSilvera KSmith JACGilman ISSage RFfalseAtmospheric CO2 decline and the timing of CAM plant evolution.<h4>Background and aims</h4>CAM photosynthesis is hypothesized to have evolved in atmospheres of low CO2 concentration in recent geological time because of its ability to concentrate CO2 around Rubisco and boost water use efficiency relative to C3 photosynthesis. We assess this hypothesis by compiling estimates of when CAM clades arose using phylogenetic chronograms for 73 CAM clades. We further consider evidence of how atmospheric CO2 affects CAM relative to C3 photosynthesis.<h4>Results</h4>Where CAM origins can be inferred, strong CAM is estimated to have appeared in the past 30 million years in 46 of 48 examined clades, after atmospheric CO2 had declined from high (near 800 ppm) to lower (<450 ppm) values. In turn, 21 of 25 clades containing CAM species (but where CAM origins are less 2023-01-01T00:00:00Z2023 Nov2025-04-25T23:29:18.232Z2025-04-06T09:22:23.699ZS-EPMC107999943764224510.1093/aob/mcad122