Murbeckiella is dead, long live Oreophyton - Origin and systematics of Tribe Oreophytoneae (Brassicaceae).

Abstract

Background and aims: The small genus Murbeckiella from the Brassicaceae family underwent manifold taxonomic changes reflecting morphological uncertainties, but also unusual biogeographic distribution patterns ranging from Spain and northern Africa to Caucasus. Close relationships with Oreophyton have been proposed, and both genera have been placed in the orphan tribe Oreophytoneae. We explore phylogenetic relationships to unravel and revise present-day taxonomic treatments, propose a biogeographic framework and contribute to our understanding of the local endemic Murbeckiella omissa from France. For detecting putative hybrids and reticulate evolutionary patterns on polyploid level the newly introduced Paralog PhyloGenomics (PPG) approach has been tested.

Methodology: Short-read whole-genome-sequencing (WGS) was used to map to a 1,000 nuclear gene target data. In addition, coding sequences from the plastome were extracted for phylogenetic reconstruction and divergence time estimates. The PPG approach was applied for phylogenetic reconstructions and evolutionary inference.

Key findings: The PPG concept resolved phylogenetic relationships among diploids and polyploids successfully. Murbeckiella appeared poly- and paraphyletic and the majority of species have been taxonomically integrated into a newly defined genus Oreophyton. One single species, Murbeckiella sousae, is placed in a clade of distinct tribe Arabideae and is awaiting future taxonomic revision. Biogeographic evidence suggests an origin of the tribe in Anatolia or adjacent Levant with crown group diversification of the different species starting with the early Pleistocene.

Conclusions: The genus Murbeckiella is a suitable system to apply WGS methods to unravel reticulate evolutionary histories of young species complexes. Its small genome allows deep sequencing at high quality, which may facilitate future studies illustrating the genomic footprints and genetic backgrounds of range expansion and transcontinental migration as well as adaptation in rapidly changing alpine environments.