Australian biogeography, climate-dependent diversification and phylogenomics of the spectacular Chamelaucieae tribe (Myrtaceae)

Chamelaucieae is a diverse tribe in Myrtaceae with ~800 species in 37 genera distributed across Australia. We applied target capture sequencing using the Angiosperms353 probe set for 131 taxa as part of the Genomics for Australian Plants initiative. Sampling all genera (36) from 10 of 11 named subtribes, we present a phylogenomic analysis for the tribe. This phylogenomic approach has allowed us to better resolve subtribal relationships across the tribe, resulting in an updated classification and additional subtribe (total of 12 subtribes including Triplarininae). Despite these advances, the phylogenetic placements of Stenostegiinae, Astarteinae, and Micromyrtinae remain equivocal and resolution of these relationships should be a focus of future research. We constructed a dated phylogeny from this genomic dataset to investigate the tribe’s biogeographic history and diversification dynamics. We estimate that the crown radiation occurred in the Eocene (c. 42 Ma), with the ancestral area of origin in Australia unresolved. Subsequent divergence and origin of subtribes mostly occurred in south-west Western Australia with frequent dispersals from there into the semi-arid and arid interior since the Miocene (20 Ma). Dispersals out of northern and eastern Australia were limited and confined to dispersal events into the arid interior. Using paleoenvironmental diversification models we show that after the initial radiation, diversification in Chamelaucieae declined rapidly until the Eocene–Oligocene boundary extinction pulse event and subsequently more slowly to the present, with a modest increase during the Middle Miocene Climatic Optimum. No significant diversification rate shifts were detected within clades except within the subtribe Chamelauciinae. There was no significant geographic-dependent diversification in the tribe. Our results add to the growing literature revealing that high plant diversity in south-west Western Australia is due to more time for species accumulation attributed to long-term climatic stability rather than elevated diversification rates.