A global bioregionalisation for orchids

Bioregionalisation is a hierarchical system that categorises geographical areas according to their biotic composition and evolutionary history. While a global bioregionalisation has been proposed for angiosperms, this is lacking for plant families with global relevance, such as orchids. We used 732 359 orchid distribution records and a phylogeny of 19 123 species to define the global bioregionalisation of orchids based on phylogenetic beta diversity at 200 × 200 km resolution. Using the resulting bioregionalisation, we analysed the environmental drivers that determine the formation of realms. Additionally, we assessed the effect of sampling completeness, different metrics, and spatial resolutions. We identified six global orchid realms (Australian, Andean-Patagonian, Neotropical, Afrotropical, Indo-Malaysian, and Holarctic) and 10 bioregions; four main transition zones were also detected. Mean annual precipitation and temperature, and precipitation and temperature seasonality, had the strongest influence on the delimitation of realms. We present a global bioregionalisation for orchids, identifying the environmental factors that determine the realms. More generally, these results highlight the importance of bioregionalisation for understanding evolutionary patterns of taxonomic families. Using a comprehensive seven-step methodology, we emphasize the need to account for sampling completeness and spatial resolution in such analyses.