This study investigates the biogeography of the Australian Camphorosmeae (Amaranthaceae s.l.) and how it relates to shifts in climatic niche and habitat types of the lineage. Building on previous research and data resources, we integrate molecular phylogenetics, bioclimatic data and biogeographic models to deepen our understanding of the diversification and adaptation of this group across Australia’s diverse landscapes in relation to palaeoclimatic changes. For 159 species representing 12 genera, georeferenced distribution points were used to define the most informative bioclimatic variables using principal component analyses. Evolutionary shifts in climatic niches and habitat types were analysed, revealing clade-specific shifts and adaptations to different habitats and climatic conditions. Biogeographic analyses allowed us to infer ancestral areas of Camphorosmeae in Australia and relate their expansion over evolutionary time to habitat shifts. Key periods of aridification in Australia, particularly during the Late Miocene to Pliocene, and the already existing adaptation of this group to warm and dry habitats, were critical in driving its diversification through migration and local adaptation to varied habitats of arid Australia. Our analyses suggest that the “Riverine Desert” habitat that existed already in the Late Miocene and “migrated” eastwards offered suitable conditions for ancestral Australian Camphorosmeae and facilitated their early widespread occurrence in the Western and Eastern Desert. We hypothesise that early diverging lineages such as Roycea adapted to the later emerging “Desert Lake” habitat when it spread in Western Australia during the Early Pliocene. Further habitat type shifts occurred from “Riverine Desert” to “Shield Plain”, “Karst Plain” and to “Sand Desert” also during the Pliocene and Pleistocene once these habitat types emerged. This research shows the complex interplay between ecological flexibility and niche conservatism in shaping the biodiversity of Australian Camphorosmeae.

C4 is one of three known photosynthetic processes of carbon fixation in flowering plants. It evolved independently more than 61 times in multiple angiosperm lineages and consists of a series of anatomical and biochemical modifications to the ancestral C3 pathway increasing plant productivity under warm and light-rich conditions. The C4 lineages of eudicots belong to seven orders and 15 families, are phylogenetically less clustered than those of monocots, and entail an enormous structural and ecological diversity. Eudicot C4 lineages likely evolved the C4 syndrome along different evolutionary paths. Therefore, a better understanding of this diversity is key to understanding the evolution of this complex trait as a whole. Compiling 1,207 recognized C4 eudicots species described in the literature and presenting trait data among these species, we identify global centres of species richness and of high phylogenetic diversity. Furthermore, we discuss climatic preferences in the context of plant functional traits. We identify two hotspots of C4 eudicot diversity: arid regions of Mexico/Southern United States and Australia, where several C4 eudicot lineages diversified independently. Further eudicot C4 hotspots with many different families and genera represented are in South Africa, West Africa, Patagonia, Central Asia and the Mediterranean. In general, C4 eudicots were abundant in deserts and xeric shrublands, tropical and subtropical grasslands, savannas and shrublands. We found C4 eudicots to occur in areas with less annual precipitation than C4 grasses which can be explained by frequently associated adaptations to drought stress such as among others succulence and salt tolerance. We conclude that in most eudicot lineages C4 evolved in ancestrally drought adapted clades and enabled these to further spread in these habitats and colonise even drier areas.