Photosynthesis metabolism in the Compositae: Current knowledge and future directions

Compositae accounts for ca. 10% of all flowering plants, being found in nearly all types of habitats worldwide. The family is particularly diverse in markedly dry and seasonal habitats, raising questions about what processes led to diversification in these challenging environments. The presence of C4 and CAM metabolism in some Compositae taxa has been known since the 1970s, and although some of these taxa have been extensively studied, such as Flaveria, there has been no systematic effort in gathering and reviewing data about photosynthesis metabolism in the family in the last few decades. In the present paper, we gathered data from more than 50 articles, spanning several different methods, raising information on photosynthesis metabolism for more than 400 Compositae species. We also present newly acquired carbon isotope data for 66 species, mostly from previously unsampled tribes. We analyzed photosynthesis metabolism in the tribe Tageteae using a phylogeny and ancestral character reconstruction. C4 photosynthesis in Compositae is restricted to two tribes: Tageteae, where it had two independent origins, and Coreopsideae, where it seems to have arisen only once. CAM metabolism is found in succulent members of tribe Senecioneae, and in Astereae and Eupatorieae, with an unknown number of evolutionary origins. We discuss the evolutionary implications of the results and propose future directions for studying photosynthesis metabolism in the family