Bricklebush (Brickellia) phylogeny reveals dimensions of the great Asteraceae radiation in Mexico

Data from molecular phylogenetics were used to assess aspects of diversity and relationships in Brickellia, a large and widespread genus of Eupatorieae. The dataset included sequence data from nuclear ribosomal ITS, ETS, and plastid psbA-trnH regions. An initial question was to assess the monophyly of the genus and whether Barroetea, Phanerostylis, and Kuhnia should be recognized as separate from or included in Brickellia. The results supported the hypothesis that Brickellia is monophyletic, with the small (2-3 species) Pleurocoronis as the sister group and showed Barroetea, Phanerostylis, and Kuhnia all embedded within the genus. Results of a time calibrated phylogeny from a BEAST analysis gave an estimated origination time for Brickellia at about 9 million years ago (Ma), with the oldest split within the genus dated at about 7.5Ma. A BAMM analysis based on the time calibrated tree showed that Brickellia has one rate shift in diversification associated with its origin in the late Miocene. Some lineages within the genus have had an increase in the rate of diversification over the past 5Ma, whereas other lineages have had a decrease in net diversification during this period. The results also elucidated nine clades within Brickellia which are accepted as taxonomic sections, and that will form logical units for future detailed studies.