The delimitation and evolutionary history of the Australasian Lautusoid group of Senecio (Asteraceae: Senecioneae)

Senecio (Asteraceae: Senecioneae) is one of the largest genera of flowering plants and its infrageneric delimitation has been impeded by its large size (> 1000 species), large morphological variation and widespread incongruence between phylogenies derived from different datasets. As part of efforts to improve our understanding of the evolutionary relationships among infrageneric Senecio groups, nuclear (nrITS, ETS) and plastid (psbA-trnH, trnL and trnL-F) DNA sequence data were used to study the delimitation of the Australasian Lautusoid group of Senecio. These data were also used to understand the evolutionary origins of polyploid species that have been placed in this informally recognized group. The results of our phylogenetic analyses indicate that Australasian Senecio compose four separate and distantly related lineages, which are here informally named the Disciform s.str., Lautusoid, Odoratus s.l., and Quadridentatus groups. A new delimitation of the Lautusoid group is presented that includes species previously placed in this group based on morphological similarities, as well as some that were previously assigned to other informally recognized Senecio groups. This brings the total number of confirmed members of the Lautusoid group to 15 species. Six allopolyploid species were identified that resulted from hybridization between members of the Lautusoid group and species of the three other Australasian Senecio lineages. Our findings indicate that hybridization has played an important role in the evolutionary diversification of Australasian Senecio and provide a framework for further studies into their evolutionary history.