Phylogenetic relationships in the southern African genus Drosanthemum (Ruschioideae, Aizoaceae)

Sigrid Liede-Schumann; Guido W Grimm; Nicolai M Nürk; Alastair J Potts; Ulrich Meve; Heidrun E K Hartmann

doi:10.7717/peerj.8999

Phylogenetic relationships in the southern African genus Drosanthemum (Ruschioideae, Aizoaceae)

PeerJ. 2020 May 8:8:e8999. doi: 10.7717/peerj.8999. eCollection 2020.

Authors

Sigrid Liede-Schumann¹, Guido W Grimm², Nicolai M Nürk¹, Alastair J Potts³, Ulrich Meve¹, Heidrun E K Hartmann⁴

Affiliations

¹ Department of Plant Systematics, University of Bayreuth, Bayreuth, Germany.
² Unaffiliated, Orléans, France.
³ African Centre for Coastal Palaeoscience, Nelson Mandela University, Port Elizabeth, Eastern Cape, South Africa.
⁴ Department of Systematics and Evolution of Plants, University of Hamburg, Hamburg, Germany.

Abstract

Background: Drosanthemum, the only genus of the tribe Drosanthemeae, is widespread over the Greater Cape Floristic Region in southern Africa. With 114 recognized species, Drosanthemum, together with the highly succulent and species-rich tribe Ruschieae, constitute the 'core ruschioids' in Aizoaceae. Within Drosanthemum, 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.

Methods: Using chloroplast and nuclear DNA sequence data, we performed network- and tree-based phylogenetic analyses of 73 species of Drosanthemum with multiple accessions for widespread species. A well-curated, geo-referenced occurrence dataset comprising the 134 genetically analysed and 863 further accessions was used to describe the distributional ranges of intrageneric lineages and the genus as a whole.

Results: Phylogenetic inference supports nine clades within Drosanthemum, seven of which group in two major clades, while the remaining two show ambiguous affinities. The nine clades are generally congruent to previously described subgenera within Drosanthemum, with exceptions such as cryptic species. In-depth analyses of sequence patterns in each gene region were used to reveal phylogenetic affinities inside the retrieved clades in more detail. We observe a complex distribution pattern including widespread, species-rich clades expanding into arid habitats of the interior (subgenera Drosanthemum p.p., Vespertina, Xamera) that are genetically and morphologically diverse. In contrast, less species-rich, genetically 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 that the main lineages arose from an initial rapid radiation, with subsequent diversification in some clades.

Keywords: Distribution; Genetic diversity; Greater Cape Floristic Region; Haplotyping; MJ Network; Maximum Likelihood; Outgroup placement; Phylogeny; SP Network; Subgeneric Classification.

Associated data

Dryad/10.5061/dryad.n2z34tms2

Grants and funding

This work was supported by two awards of the Mesemb Study Group (M.S.G.) in 2010 and 2013. The publication of this work was funded by the German Research Foundation (DFG) and the University of Bayreuth in the funding programme Open Access Publishing. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.