| Summary: | Background: CAM photosynthesis is a successful adaptation that has evolved often in angiosperms, gymnosperms, ferns and lycophytes. Present in ca. 5 % of vascular plants, the CAM diaspora includes all continents barring Antarctica. Species with CAM inhabit most landscapes colonized by vascular plants, from the Arctic Circle to Tierra del Fuego, from below sea-level to 4,800 m, from rainforests to deserts. They have colonised terrestrial, epiphytic, lithophytic, palustrine and aquatic systems developing perennial, annual or geophyte strategies that may be structurally arborescent, shrub, forb, cladode, epiphyte, vine or leafless with photosynthetic roots. CAM may enhance survival by conserving water, trapping carbon, reducing carbon loss and/or via photoprotection. Scope: This review assesses the phylogenetic diversity and historical biogeography of selected lineages with CAM viz. ferns, gymnosperms and eumagnoliids, Orchidaceae, Bromeliaceae, Crassulaceae, Euphorbiaceae, Aizoaceae, Portulacineae (Montiaceae, Basellaceae, Halophytaceae, Didiereaceae, Talinaceae, Portulacaceae, Anacampserotaceae, Cactaceae) and aquatics. Conclusions: Most extant CAM lineages diversified since the Oligocene/Miocene as the planet dried and CO2 concentrations dropped. Radiations exploited changing ecological landscapes including Andean emergence, Panamanian Isthmus closure, Sundaland emergence and submergence, changing climates and desertification. Evidence remains sparse for or against theories that CAM-biochemistry tends to evolve prior to pronounced changes in anatomy, and that CAM tends to be a culminating xerophytic trait. In perennial taxa, any form of CAM may occur depending upon the lineage and the habitat, although facultative CAM appears uncommon in epiphytes. CAM annuals lack strong CAM. In CAM annuals, C3+CAM predominates and inducible- or facultative- CAM are common.
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