Despite the richness of the Cape Flora, there are relatively few published phylogenetic studies that investigate the origins of this diversity. To address this, we estimated the phylogeny of a Cape grass genus, Ehrharta, and used this to investigate its past diversification. With 24 species, Ehrharta is much larger than any other genus in its tribe, and shows a remarkable diversity of form and ecological function that suggests adaptive radiation. Our phylogenetic analyses included representatives of all four ehrharteoid genera, and used three data sources: two molecular (ITS1 and trnL-F) and one morphological. The results confirm the monophyly of Cape Ehrharta species and provide a framework for reconstructing historical shifts in the edaphic and climatic niches occupied by the genus in the western Cape. Habitat reconstruction suggests that the major diversification of the genus followed movement into habitats experiencing more intense and prolonged summer aridity than those inferred to be ancestral. At least some speciation within the Cape arid zone may be linked to greater edaphic diversity here.

Key words: Cape Flora, Ehrharta, Poaceae, radiation