Diversification of Camphorosmeae (Amaranthaceae s.l.) during the Miocene-Pliocene aridification of inland Australia

The Australian Camphorosmeae represent a monophyletic lineage that diversified to include ca. 150 spp. across 12 genera, and populate large parts of arid Australia. Tracking the origin and spread of this ancestrally salt and drought tolerant lineage provides additional evidence about the timing of the evolutionary history and phylogenetic assembly of arid habitats in Australia. Using a customized RADseq approach, sequence data for 104 species of the Australian Camphorosmeae representing all 12 genera were generated and included in phylogenetic and dating analyses. Furthermore, habitat type occurrences and preferences of species and clades were recorded. As suspected, the characters used to delimit current Australian Camphorosmeae genera do not support monophyletic groups, as phylogenetic analyses yielded 17 statistically supported clades across a large Maireana grade and crown radiation of Sclerolaena. The diversification of Australian Camphorosmeae is clearly linked to landscape changes and emerging new habitat types in arid Australia since the ancestral element likely arrived from temperate semi-arid to arid parts of continental Eurasia in the Middle Miocene. Migration was likely multidirectional and followed a west-to-east aridification. Crown group diversification was strongest during the Pliocene and likely promoted by the west-to-east expansion of Riverine Desert habitats and subsequent expansion and colonization of newly developing arid habitats. Rapid range expansion, fast habitat saturation, as well as periodic expansion, contraction and replacement of arid habitats, may have caused the rather species-poor clades of the earlier-divergent Maireana grade, compared to the continuously diversifying Sclerolaena clade.