Evolution of the Resin Daisies: Biogeography of the Genus <i>Pteronia</i> L. (Astereae, Asteraceae) in the Arid and Semi‐Arid Habitats of Southern Africa

ABSTRACT Aim The species‐rich flora of southern Africa results from Neogene species accumulation involving multiple geographically distinct radiations. This diversity was enhanced by lineage cross‐seeding amongst several broadly defined regional floras. We examine the relative ages and the role of shifts between southern African habitats in the Desert and Fynbos floras in a single lineage of Cape daisies, the resin daisy genus Pteronia . Using these xeric‐adapted shrublets, we more finely dissect the radiations to explore the relative ages of occupation and diversification in the different winter‐rainfall floras of South Africa (fynbos, renosterveld, and succulent karoo vegetation), as well as the adjacent arid and semi‐arid Desert, Nama Karoo and Kalahari Savanna floras. Location Southern Africa, focusing on the winter‐rainfall floras and adjacent arid/semi‐arid regions in the south‐western corner of the subcontinent. Methods A dated species‐level molecular phylogenetic hypothesis for Pteronia and outgroups is presented. Eight floristic and biogeographic areas of distribution are identified. Ancestral areas and the timing, frequency, and direction of range change events amongst these areas are inferred using the statistical DEC model on a sample of dated posterior trees. Results Pteronia is strongly supported as monophyletic and began diversifying in the late Miocene, consistent with other Cape radiations, particularly those associated with arid regions. From the ancestral range of the genus in the northern parts of the Succulent Karoo and/or fynbos vegetation, the first novel vegetation type to be colonised was Nama Karoo at the end of the Miocene, followed by south‐eastern Succulent Karoo, renosterveld in the early Pliocene, and Kalahari Savanna in the Late Pliocene. The subtropical thicket and Bushmanland bioregions were colonised more recently in the Pleistocene. Early diversification in Pteronia gave rise to two lineages. The first lineage diversified in and remains strongly confined to the northern Succulent Karoo. The second lineage diversified in both fynbos and a range of adjacent arid/semi‐arid vegetation types, experiencing more frequent shifts between habitat types. Main Conclusions Speciation in Pteronia is associated with two geographic patterns: firstly, diversification within single habitat types, which applies to the northern succulent karoo and to a lesser extent, the fynbos vegetation, and secondly, diversification associated with shifts between habitat types. Habitat shifts appear to be strongly influenced by habitat adjacency and ecological similarity. Understanding the nature and timing of historical habitat shifts in Pteronia may contribute to the knowledge of interactions between different floras within South Africa, both winter and summer rainfall, as well as the timing of colonisation of these areas, particularly the Succulent and Nama Karoo.