A phylogeny of the Gochnatieae: Understanding a critically placed tribe in the Compositae

Abstract

Subfamily Gochnatioideae is the sister group of similar to 96% of the species in Compositae (Asteraceae). It is of particular interest not only because of its position in the phylogeny, but also because, in recent molecular studies, the node it occupies is not strongly supported making difficult any inferences on the direction of character evolution in the family. The recognition of tribe Gochnatieae was one of the results of a comprehensive molecular analysis of the family that showed the traditional circumscription of the Mutisieae to be non-monophyletic. The four genera of Gochnatieae (Cnicothamnus, Cyclolepis, Gochnatia, Richterago) were defined by the presence of apiculate anther appendages and dorsally smooth style branches. Gochnatia, which contained about 70 species, was the largest and most complex genus and in the last decade some of its sections have been moved (or returned) to the rank of genus. This study includes a large selection of potential outgroups and over 60% of all species in the tribe, including all the genera and all but one of the sections of Gochnatia, to examine evolutionary relationships among the taxa. Both cpDNA and nrDNA were used in a phylogenetic analysis using parsimony, likelihood, and Bayesian approaches. The results suggest a non-monophyletic Gochnatia that is here resolved by the recognition of segregate genera. Morphological characters support these new genera and allow the adoption of a new classification for the Gochnatieae. A biogeographic analysis shows a possible southern South American/Andean origin followed by movement in three directions: into the Central Andes, into central and northern Brazil, and into Mexico and the Caribbean. The dating analysis gives an age of the split of the core Gochnatieae from the Wunderlichieae-Cyclolepis clade, and hence the age of the tribe, of 36-45 Ma and an age of 23-25 Ma for the first split within the core Gochnatieae (Andean vs. Brazil-Mexico-Caribbean). Cnicothamnus remains in Gochnatieae but Cyclolepis is designated incertae sedis.