Phylogenetics, diversification, and biogeography of Azorella (Apiaceae), with a special focus on the Australasian clades

Abstract To expand on prior evolutionary studies conducted on the genus Azorella (Apiaceae), we here present analyses based on more intensive sampling from Australasian representatives of the genus, which had been less thoroughly represented in the prior studies, especially species from section Schizeilema , a group largely native to New Zealand. In this study, 144 specimens representing 56 of the 57 recognized species and putatively new species were sampled for nine DNA sequence regions from the plastid genome and two regions from the nuclear genome. The study also provides deeper analyses of biogeography (DEC model selected by BioGeoBears + ModelTest in RASP 4), divergence (BEAST), and diversification (RevBayes) compared to prior work. Our phylogenetic analyses corroborated earlier results regarding the relationships among the ten sections of Azorella and provided stronger evidence for other relationships that had been less well established. Incongruencies between phylogenetic trees based on plastid and nuclear data suggest reticulation events within the group, especially regarding the origin of section Schizeilema and among the subclades within that section, where speciation by hybridization and polyploidy appears common. The two nuclear datasets provide evidence of nonuniform concerted evolution and incongruence among sections Ranunculus , Schizeilema , and Stilbocarpa . These analyses also suggest that the origin and diversification of Azorella has been affected by events related to the cooling and break up of Antarctica during the Oligocene. Since that time, parallel dispersals to and radiations in Australasia (especially New Zealand) and the Andes have occurred, and that diversification rates accelerated during the Pliocene and Pleistocene concurrent with the opening of new high-altitude ecological niches in New Zealand’s Southern Alps and the Andes of South American.