Phylogenetics and taxonomy of the Gorteria clade (Asteraceae-Arctotideae)

Abstract: This thesis deals with the systematics of the Gorteria-Gazania-Hirpicium-clade within the tribe Arctotideae-Gorteriinae in the angiosperm family Asteraceae. The group is found in southern Africa, with many representatives in the Greater Cape Floristic Region in South Africa, an area known for its high species richness and endemism. Specifically, species delimitation within Gorteria and its intergeneric relationships to Hirpicium and Gazania were investigated.Previous phylogenetical studies showed that the two shrubby Hirpicium alienatum and H. integrifolium were more closely related to the herbaceous genus Gorteria than to remaining species of Hirpicium. During field studies additional proof of their affinity was found when these two, like Gorteria, were found to have capitulum diaspores.Gorteria was phylogenetically investigated with a large number of samples from different populations of G. diffusa, a species showing striking variation in ray floret coloration. The study showed that the current division of the genus into three species (Gorteria corymbosa, G. diffusa and G. personata) was not supported and it was also shown that the two Hirpicium species were not sister to but nested within a paraphyletic Gorteria. The necessary nomenclatural changes were made including the new combination Gorteria alienata but left remaining species of Hirpicium unassigned to a genus because the type of Hirpicium was included in Gorteria.When the intergeneric relationship between Gorteria, Gazania and the remaining species of Hirpicium were investigated in detail it was shown that an additional four species of Hirpicium had also evolved from an ancestor within Gorteria. The generic name Berkheyopsis was resurrected for the morphologically deviating Hirpicium echinus while a new genus, Roessleria, was described for the remaining species of Hirpicium. There was high support for a monophyletic Gazania even though the relationship among the genera was unresolved.