The Greater Yellowstone region has few endemic plant species, or species that occur only in Yellowstone and nowhere else in the world. Endemic species occur in unusual or specialized habitats such as hydrothermal areas. Within Yellowstone, only three endemic species occur: Ross’s bentgrass (Agrostis rossiae), Yellowstone sand verbena (Abronia ammophila), and Yellowstone sulfur wild buckwheat (Eriogonum umbellatum var. cladophorum).
Several other unusual species live in the Greater Yellowstone Area: warm springs spike rush, which grows in warm water; and Tweedy’s rush, sometimes the only vascular plant growing in acidic hydrothermal areas.