A Plant-Diversity Dark Spot at the Intersection of Three Biodiversity Hotspots: Environmental Drivers of Brassicaceae Richness in Türkiye.

We provide the first nationwide, spatially explicit analytical framework for assessing how environmental and spatial processes structure species and endemic richness in Brassicaceae across Türkiye, a global plant-diversity "dark spot." We compiled an updated national checklist and > 15,000 unique, georeferenced herbarium records for Brassicaceae and aggregated them to 0.5° × 0.5° grid cells. We quantified species and endemic richness per cell and related them to contemporary climate, aridity, long-term climatic stability, net primary productivity, human modification, and topography. We compared ordinary least squares with spatial regression models, performed variation partitioning to separate environmental and spatial components, and applied geographically weighted regression to assess spatial variation in relationships. In doing so, we found that species and endemic richness peak in southern Anatolia (the Western and Central Taurus Mountains) and along the Anatolian Diagonal, with additional species-rich areas in the northern parts of the Central Anatolian Plateau. For species richness, topographic roughness has a strong positive effect, whereas annual precipitation has a strong negative effect, consistent with concentration in topographically heterogeneous, relatively dry landscapes. For endemic richness, elevation and roughness have strong positive effects, whereas temperature, past-climatic stability index, and aridity index have strong negative effects, indicating that endemics are concentrated in high-elevation, topographically heterogeneous, cooler, climatically stable, and relatively dry landscapes. Environmental gradients explain substantially more variation than purely spatial structure, and geographically weighted regression shows that model fit is highest in the Central Taurus Mountains. Overall, topographically complex, climatically stable mountain systems in southern Anatolia and along the Anatolian Diagonal simultaneously act as centers of species and endemic richness in Brassicaceae. These regions emerge as key conservation priorities for safeguarding both current diversity and evolutionary potential in one of the world's plant-diversity "dark spots".