Vascular plant flora of the alpine zone in the southern Rocky Mountains, U.S.A

Field detection of changes in occurrence, distribution, or abundance of alpine plant species is predicated on knowledge of which species are in specific locations. The alpine zone of the Southern Rocky Mountain Region has been systematically inventoried by the staff and floristics graduate students from the Rocky Mountain Herbarium over the last 27 years. It is centered on the mountain ranges of Colorado and extends north to the Medicine Bow Mountains in southeast Wyoming and south into the Sangre de Cristo Range in north central New Mexico. It also includes the La Sal Mountains of Utah and the San Francisco Peaks in northern Arizona. The alpine meadow and treeline ecotone flora of the Southern Rocky Mountains includes 609 unique taxa of vascular plants comprising 581 species. The richest families are Asteraceae (104 species), Poaceae (58 species), Cyperaceae (57 species), and Brassicaceae (42 species). The central Colorado subregion is the most taxon rich (499) with richness tapering off to the north, southeast, and southwest. Non-endemic alpine zone taxa occur more frequently elsewhere in the Rocky Mountain Cordillera Floristic Region (515) than in the Madrean (373), Circumboreal (226), or North American Atlantic Floristic Regions (120). Levels of endemism within the flora of the alpine zone in the Southern Rocky Mountains range from single mountains (7) to the flora as a whole (59) including 25 taxa endemic to both the Southern Rockies and to its alpine zone. This checklist is based on vouchered specimens and should be most useful to botanists and land managers determining what taxa are likely to occur within their area of interest.