Revised Taxonomy of the Arctotis Annual Clade (Arctotideae, Asteraceae) from Southern Africa: Integration of Molecular Phylogenetic and Morphological Evidence

Previous phylogenetic analysis of ITS nrDNA sequence data for Arctotidinae species resolved a strongly supported clade containing all but one of the showy annual Arctotis species (informally designated the Arctotis Annual Clade). In the present study, phylogenetic relationships in the Arctotis Annual Clade were investigated by Bayesian inference and maximum parsimony analyses of cpDNA (trnT-trnL-trnF and trnH-psbA) and nrDNA (ITS) sequence data. The cpDNA and nrDNA phylogenies were notably incongruent. Arctotis venusta and a putative unnamed species (A. ‘sp. B’) were strongly supported as monophyletic by both data sets. The monophyly of A. leiocarpa was strongly supported by the ITS data set, whereas the remaining accessions formed a poorly resolved complex (the ‘A. fastuosa complex’). Within the A. fastuosa complex, A. hirsuta was monophyletic with strong support in the ITS phylogeny. A statistical parsimony-derived cpDNA haplotype network resolved five broad groups of haplotypes and showed no consistent geographical structure, but species-specific haplotype lineages for A. venusta and A. sp. B were resolved. Arctotis fastuosa accessions were distributed among four haplotype groups. Incongruence between the data sets and poor resolution within the A. fastuosa complex may reflect reticulate evolution, ancestral polymorphism, and incomplete lineage sorting, in tandem with the low information content of the data sets. The greatest phenotypic diversification in the clade is in cypsela morphology. Comparison of cypsela morphology with the phylogenies suggests a general trend for reduction in the sizes of the cypsela, abaxial wings, pappus scales, and loss of pubescence during diversification. A revised taxonomy, integrating currently available evidence, accompanied by full descriptive accounts and a key to the taxa are presented. Eight species are recognized, including the nomenclatural novelties Arctotis chrysantha (sp. nov.) and Arctotis namibiensis (sp. nov.). The names Arctotis karasmontana, Venidium fugax, and Venidium macrocephalum are lectotypified.