Phylogenetic relationships in the southern African genusDrosanthemum(Ruschioideae, Aizoaceae)

Abstract

AbstractBackgroundDrosanthemum,the only genus of the tribe Drosanthemeae, is widespread over the Greater Cape Floristic Region in southern Africa. With 114 recognized species,Drosanthemumtogether with the highly succulent and species-rich tribe Ruschieae constitute the ‘core ruschioids’ in Aizoaceae. WithinDrosanthemum, nine subgenera have been described based on flower and fruit morphology. Their phylogenetic relationships, however, have not yet been investigated, hampering understanding of monophyletic entities and patterns of geographic distribution.MethodsUsing chloroplast and nuclear DNA sequence data, we performed network- and tree-based phylogenetic analyses of 73 species represented by multiple accessions ofDrosanthemum. A well-curated, geo-referenced occurrence data set comprising the phylogenetically studied and 867 further accessions was used to describe the distributional ranges of intrageneric lineages and the genus as a whole.ResultsPhylogenetic inference supports nine clades withinDrosanthemum, seven of them group in two major clades, while the remaining two show ambiguous affinities. The nine clades are generally congruent to previously described subgenera withinDrosanthemum, with exceptions such as (pseudo-) cryptic species. In-depth analyses of sequence patterns in each gene region revealed phylogenetic affinities not obvious in the phylogenetic tree. We observe a complex distribution pattern including widespread, species-rich clades expanding into arid habitats of the interior (subgeneraDrosanthemump.p., Vespertina, Xamera) that are molecular and morphologically diverse. In contrast, less species-rich, molecularly less divergent, and morphologically unique lineages are restricted to the central Cape region and more mesic conditions (Decidua,Necopina, Ossicula, Quastea, Quadrata, Speciosa). Our results suggest initial rapid radiation generating the main lineages, with some clades showing subsequent diversification.