Phylogenetic and Biogeographic Insights into the Reproductive Evolution and Taxonomy of Australasian Teucrium (Lamiaceae)

Reproductive systems in Lamiaceae typically consist of bilabiate zygomorphic flowers and dry mericarp fruit, therefore examining deviations from this strategy contributes to our understanding of evolution. Teucrium L. (Lamiaceae: Ajugoideae) is easily recognised by the unilabiate flower. The genus is cosmopolitan but most speciose in the Mediterranean region. Previous phylogenetic analysis showing three segregate genera nested within Teucrium raises questions about the taxon's dispersal throughout the region and the distinctive morphological changes. We conducted phylogenomic analyses of nuclear genes sequenced by targeted enrichment (Angiosperms353) for all Australasian species, phrase names and outgroups (39 total). Results show high support for most species clades and unequivocally place most 'unknowns' in context with other described taxa. Australasian Teucrium constitute at least two distantly related clades. The most speciose, with a crown age of 10.2-14.8 Ma, is widespread across Australia and includes an arid-adapted lineage that evolved actinomorphic corollas and fleshy fruits. The second clade of three eastern Australian species has a crown age of 5.9-12.2 Ma that corresponds best with dispersal associated with the Sunda-Sahul collision. Our results highlight repeated colonisation of Teucrium in Australia and corresponding shifts towards animal dispersal that took place as early as c. 9.2 Ma.