A phylogenetic investigation of the taxonomically problematic Eucalyptus odorata complex (E. section Adnataria series Subbuxeales): evidence for extensive interspecific gene flow and reticulate evolution

ABSTRACT To investigate the relationships among species in the taxonomically problematic Eucalyptus odorata species complex, we generated molecular data using double-digest restriction site-associated DNA sequencing (ddRADseq) and Diversity Arrays Technology sequencing (DArTseq). These data were analysed utilising principal-component analysis (PCA), phylogenetic networks, phylogeny reconstruction and hybridisation tests. Twelve species that are variously recognised in the complex were sampled from across their ranges, along with co-occurring members of E. section Adnataria, to allow for patterns of hybridisation and gene flow to be identified. Despite the large genetic datasets generated, many relationships within the E. odorata complex were poorly resolved, and few species were monophyletic, likely owing to both biological factors including recent speciation and extensive hybridisation and introgression, and potential over-splitting of taxa. We show that multiple taxa with limited distributions are the result of reticulate evolutionary events and that typical Eucalyptus viridis R.T.Baker and the possibly con-specific E. aenea K.D.Hill are sister to the rest of the complex. The remaining species appeared to represent a discontinuous crescent-shaped cline running from the Flinders Ranges to the south-western slopes region of New South Wales, with limited support for an east–west split in this cline across the Murray River Basin. Eucalytpus viridis var. latiuscula Blakely, which is not closely related to the typical variety of this species in our data, may represent a northern extension to this cline.