CAPITULUM: The International Compositae Alliance Newsletter

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

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

Kenneth C. Oberlander

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

Nigel P. Barker

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

DOI: https://doi.org/10.53875/capitulum.01.2.05

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

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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.