Kerr, Malin SofiaA phylogenetic and biogeographic analysis of the tribe Sanguisorbeae (Rosaceae) was conducted with emphasis on the radiation of the Andean tree Polylepis. Phylogenetic analyses of coding and non-coding nuclear markers reveal a complex evolutionary history of the tribe including ancient and recent allopolyploid hybridization. Sanguisorba sensu lato is shown to be paraphyletic and split between the allopolyploid hybrid Sanguisorba and the non-hybrid Poterium and Poteridium. A monophyletic origin of the southern hemispheric subtribe Sanguisorbinae is supported, and this clade is given a phylogentic taxon name (Verruchaena). Dating analyses using the penalized likelihood method suggest that this taxon originated in the late Miocene. A biogeographic hypothesis is presented in which Verruchaena originated in the New World with subsequent transoceanic dispersals to southern Africa and Australasia. The paramo genus Polylepis most likely arose from hybridization between two Andean ancestors supporting a "vertical" rather than "horizontal" origin of this taxon.en-USDissertationBiology, BotanySanguisorbeaePolylepisRosaceaeallopolyploidyhybridizationAdh