Forming a natural barrier between the Mediterranean Basin and the dry plateaus of Western Asia, the mountains and basins that make up the Irano-Anatolian Hotspot contain many centers of local endemism. Nearly 400 plant species are found only along the Anatolian Diagonal, a floristic line that crosses Inner Anatolia; many of Turkey’s 1,200 endemic species occur only to the immediate east or west of it. The hotspot includes four endemic and threatened species of viper.