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

Robert J. McKenzie

Department of Plant Sciences and Afromontane Research Unit, University of the Free State, Private Bag X13, Phuthaditjhaba, 9866, South Africa

https://orcid.org/0000-0001-7054-3308

Kenneth C. Oberlander

H.G.W.J. Schweickerdt Herbarium, Department of Plant and Soil Sciences, University of Pretoria, Pretoria, South Africa

https://orcid.org/0000-0001-6248-351X

Nigel P. Barker

Department of Plant and Soil Sciences, University of Pretoria, Pretoria, South Africa

https://orcid.org/0000-0002-4612-1399

DOI: http://dx.doi.org/10.53875/capitulum.01.2.05

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 supported basal nodes and a haplotype network suggests a degree of taxonomic structure to cpDNA diversity. Further 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.

Keywords: biogeography, Namaqualand, Namibia, South Africa, taxonomy