This study quantifies the geographic patterns of endemism-scaled richness ("endemism richness") of vascular plants across 90 terrestrial biogeographic regions, including islands, and evaluates its congruence with terrestrial vertebrates. The results show that endemism richness of plants and vertebrates is strongly related, with values on islands being significantly higher than those on mainland regions. Specifically, endemism richness is 9.5 times higher on islands for plants and 8.1 times higher for vertebrates compared to mainland regions. The study also reveals marked differences in human impact and land cover change between island and mainland regions, with islands experiencing higher current threats and projected land-use-driven changes. Given their high levels of endemism and conservation risks, islands are identified as particularly important for species conservation efforts and warrant high priority in global biodiversity conservation. The findings highlight the need for expanded protected area networks and effective measures to address invasive species threats in island regions.This study quantifies the geographic patterns of endemism-scaled richness ("endemism richness") of vascular plants across 90 terrestrial biogeographic regions, including islands, and evaluates its congruence with terrestrial vertebrates. The results show that endemism richness of plants and vertebrates is strongly related, with values on islands being significantly higher than those on mainland regions. Specifically, endemism richness is 9.5 times higher on islands for plants and 8.1 times higher for vertebrates compared to mainland regions. The study also reveals marked differences in human impact and land cover change between island and mainland regions, with islands experiencing higher current threats and projected land-use-driven changes. Given their high levels of endemism and conservation risks, islands are identified as particularly important for species conservation efforts and warrant high priority in global biodiversity conservation. The findings highlight the need for expanded protected area networks and effective measures to address invasive species threats in island regions.