Phylogeny of Flaveria (Asteraceae) and inference of C4 photosynthesis evolution

A well-resolved phylogeny of Flaveria is used to infer evolutionary relationships among species, biogeographical distributions, and C-4 photosynthetic evolution. Data on morphology, life history, and DNA sequences (chloroplastic trnL-F, nuclear ITS and ETS) for 21 of 23 known species were collected. Each data set was analyzed separately and in combination using maximum parsimony and Bayesian analyses. The phylogeny of Flaveria is based on the combined analysis of all data. Our phylogenetic evidence indicates that C-3 Flaveria are all basal to intermediate (C-3-C-4 and C-4-like) and fully expressed C-4 Flaveria species. Two strongly supported clades (A and B) are present. Using this phylogeny, we evaluate the current systematics of the genus and suggest the removal and reevaluation of certain taxa. We also infer the center of origin and dispersal of Flaveria species. Multiple origins of photosynthetic pathway intermediacy in Flaveria are recognized. C-3-C-4 intermediacy has evolved twice in the genus and is found to be evolutionarily intermediate in clade A, but not necessarily in clade B. C-4-like photosynthesis is also derived once in each clade. In addition, fully expressed C-4 photosynthesis may have evolved up to three times within clade A.