Relationships and evolution in the Drakensberg near-endemic genus, Craterocapsa (Campanulaceae)

Abstract

The Drakensberg near-endemic genus Craterocapsa of the Campanulaceae comprises four species as circumscribed by Hilliard & Burtt with a fifth, Craterocapsa alfredica, recently distinguished from Craterocapsa insizwae based on dubious and variable morphological characters. A phylogenetic study of the relationships and evolutionary trends in Craterocapsa was undertaken based on morphological and DNA sequence data (the nuclear ribosomal ITS and the plastid trnL–trnF regions). An additional aim was to investigate the status of the various species in the genus. The generic circumscription of Craterocapsa was supported, however there is a lack of morphological evidence for the recognition of C. alfredica as a distinct taxon, and topologies of the molecular phylogenies suggest hybridisation and/or introgression as likely processes for its origin. C. alfredica is therefore here excluded from the genus. The morphological and molecular phylogenies are highly incongruent, suggesting convergence in features such as growth form and leaf shape in response to environmental factors, most notably altitude. The widespread Craterocapsa tarsodes is the first species to diverge, with dispersal northwards to Mount Inyangani a likely explanation for its highly disjunct distribution. C. insizwae and C. tarsodes are hypothesised to have speciated sympatrically in the Kokstad–Weza region, a ‘hotspot’ for the genus, whereas the sister species Craterocapsa montana and Craterocapsa congesta appear to have diverged in allopatry with ecological speciation playing a role.