Big trees of small baskets: phylogeny of the Australian genus Spyridium (Rhamnaceae: Pomaderreae), focusing on biogeographic patterns and species circumscriptions

Spyridium Fenzl is a genus of similar to 45 species endemic to south-western and south-eastern Australia. This study provides the most comprehensive phylogenies of Spyridium to date, analysing both entire chloroplast genomes and the nuclear ribosomal array (185-5.8S-26S). There was substantial incongruence between the chloroplast and nuclear phylogenies, creating phylogenetic uncertainty, but some clear relationships and biogeographic patterns could be established. Analyses support the monophyly of Spyridium, identifying an early east-west split at the base of the nuclear phylogeny and deep divergences of New South Wales and Tasmanian endemic clades. We also found evidence of more recent dispersal events between eastern and western Australia and between Tasmania and the mainland. Eleven taxa were found to be monophyletic in the nrDNA phylogeny and two were clearly polyphyletic (S. eriocephalum Fenzl and S. phylicoides Reissek). Although the polyphyly of S. eriocephalum correlates with the two varieties, suggesting distinct taxa, further research is required on S. phylicoides.

Automated summary

This study provides comprehensive phylogenetic analyses of Spyridium plants using both chloroplast genomes and nuclear ribosomal arrays. The results reveal the diversity and biogeographic patterns of Spyridium, including the monophyly of the genus, east-west split, and recent dispersal events.