A global phylogenetic regionalisation of vascular plants reveals a deep split between Gondwanan and Laurasian biotas

Abstract

Existing global regionalisation schemes for plants consider the compositional affinities among biotas, but these have not considered phylogenetic information explicitly. Incorporating phylogenetic information may substantially advance our understanding of the relationships among regions and the synopsis of biogeographical schemes, because phylogeny captures information on the evolutionary history of taxa. Here, we present the first phytogeographical delineation of the global vascular flora based on the evolutionary relationships of species. We analysed 8,738,520 geographical occurrence records for vascular plant species together with a time-calibrated phylogenetic tree including 67,420 species. We estimated species composition within 200 x 200 km grid cells across the world, and used a metric of phylogenetic beta diversity to generate a phylogenetic delineation of floristic regions. We contrasted these results with a regionalisation generated using a taxonomic beta diversity metric. We identified 16 phylogenetically distinct phytogeographical units, deeply split into two main clusters that broadly correspond to the Laurasia-Gondwana separation. Our regionalisation broadly matches currently recognized phytogeographical classifications, but also highlights that the Gondwanan area is split into a large Holotropical cluster and an Australian-NeoZelandic-Patagonian cluster. In turn, we found that the northernmost and southernmost units have the most evolutionarily distinct vascular plant assemblages. In contrast, taxonomic dissimilarity returned a regionalisation composed of 23 units with a high degree of shared taxa between Laurasian and Gondwanan areas, with no clear split among their biotas. The integration of phylogenetic information provided new insights into the historical relationships among phytogeographical units, enabling the identification of three large, clearly differentiated biotas, here referred to as kingdoms: Holarctic, Holotropical, and Austral. Our regionalization scheme provides further evidence for delineating transition zones between the Holarctic and Holotropical kingdoms. The latitudinal patterns of evolutionary distinctiveness of vascular plant assemblages are consistent with recent evidence of higher and more recent diversification of flowering plants outside tropical regions.