Phylogeny of the Dorotheantheae (Aizoaceae), a tribe of succulent annuals

Dorotheantheae (Aizoaceae) is a small tribe of succulent annual herbs with flat leaves belonging to the genera Aethephyllum, Cleretum and Dorotheanthus, which are endemic to the winter–rainfall region of South Africa. Several species are well–known for their conspicuous and striking flowers but others possess very inconspicuous flowers. Analysis of molecular data from combined plastid and nuclear sequences shows that Dorotheanthus is monophyletic while Cleretum is diphyletic, since the two species of Cleretum with lyrate leaves are most closely related to the vegetatively similar, monotypic Aethephyl–lum. In the absence of clear, diagnostic characteristics for separating Cleretum and Dorotheanthus, a revised classification for the Dorotheantheae is proposed in which the tribe consists of a single genus, Cleretum. Within Cleretum, we recognize 14 species, by raising/re–instating two subspecies to species rank and including two that are still undescribed. The major clades occupy distinct climatic and edaphic niches. Repeated shifting from large to small flowers may indicate changes in the breeding system. Since succulence in annuals is rare in the winter–rainfall region of southern Africa, we compare patterns of distribution between Dorotheantheae and the other leaf–succulent annuals in the region, namely in Mesembryanthemum (Aizoaceae) and in Crassula (Crassulaceae). We find that similar to the non–succulent annuals of the Poaceae and the Brassicaceae in this region, the annual species of Mesembryanthemum show a preference for arid areas. In contrast, in Dorotheantheae and in Crassula the hot–spots of diversity lie mainly in the wetter parts of the winter–rainfall area, with a decrease in the number of annual species northwards to the arid, winter–rainfall areas of the Richtersveld and the southern Namib.