Monarchs in the veld: The Arctotis Annual Clade provides insight into recent floristic diversification in a semi-arid region of southern Africa

Abstract

A revision of the main clade of annual species of Arctotis L. recognises eight species. All but one taxa are distributed in the winter and/or year-round rainfall regions of southern Africa, with the highest species diversity in semi-arid areas. Altitude and several temperature and precipitation parameters best explain latitudinal and longitudinal gradients in the distribution of taxa. Cypsela and pappus morphology suggest adaptation for reduced dispersibility in a semi-arid environment during diversification. Phylogenetic analyses of ITS and noncoding cpDNA sequence data resolve strongly suppor ted basal nodes and a haplotype network suggests a degree of taxonomic structure to cpDNA diversity. Fur ther research to resolve a genetically diverse "A. fastuosa species complex" is required. Diversification of the clade is not explainable solely by a simple vicariance model with parapatric speciation. A biogeographic hypothesis for diversification of the clade is formulated for future testing.