Aim: It is well known that the distribution of species diversity is spatially heterogeneous, but understanding the factors contributing to this heterogeneity and to the formation of biodiversity hotspots remains a challenge. Here, we seek to improve our understanding of how historical, ecological and evolutionary processes contribute to current patterns of global fern diversity.Location: Worldwide. Taxon: Ferns.Methods: To evaluate the drivers of global fern diversity, we integrate over 800,000 georeferenced species occurrence records of nearly 8000 species, a time-calibrated phylogeny and seven climate and environmental layers. We use these data to summarize diversity and evolutionary patterns at a resolution of 100 × 100 km, and identify hotspots of fern species richness and endemism. We compare these hotspots to neighbouring non-hotspot regions to provide insight into the factors controlling global patterns of fern diversity.Results: Tropical and subtropical mountains harbour a disproportionate amount of species relative to the land area they occupy; 58% of global species richness occur in eight principally montane hotspots together comprising just 7% of Earth's land area.We identify hotspots of fern species richness and endemism that are universally characterized by disproportionately high ecological variation. We demonstrate that total fern species richness scales linearly with available climate space at regional and global scales.Main Conclusions: Areas of high environmental heterogeneity harbour a disproportionate amount of fern species, and global patterns of extant fern diversity reflect the distribution of these areas, especially in mountains at lower latitudes. Persistence of ancient lineages in areas with long-term climatic stability helps explain exceptional endemism in regions such as Malesia.

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