The majority of these are plants with affinities to the Great Basin floristic province. They are more common in Wyoming and Utah but reach the northern margin of their range in the South Pryor Mountains area. These include Astragalus aretioides, Astragalus geyeri, Boechera demissa, Camissonia andina, Camissonia parvula, Cleome lutea, Eriogonum salsuginosum, Grayia spinosa, Leptodactylon caespitosum, Malacothrix torreyi, Mentzelia pumila, Nama densum, Stipa lettermanii, and the lichen, Rhizoplaca haydenii. Five species of vascular plants in the IPA are globally rare, being endemic to the north end of the Bighorn Basin of Montana and Wyoming: Erigeron allocotus, Penstemon caryi, Physaria lesicii, Shoshonea pulvinata, and Sullivantia hapemanii. The IPA encompasses the entire known range or a significant portion of the known populations of these species within Montana.

The South Pryor Mountains IPA has 5,000 ft of vertical relief and supports ca. 29 distinct plant communities. Forests and woodlands dominated by limber pine occur on warm, often exposed, stony-soil slopes at or above 6,500 ft. Douglas-fir forests occur on slopes at 5,000-7,000 ft. Woodlands dominated by Utah juniper occur on shallow, calcareous soil of slopes and ridges at 4,000-6,000 ft. Limber pine-juniper woodlands are found on shallow, calcareous soils of slopes between 4,000 ft and 5,300 ft. Shrublands dominated by black sagebrush and big sagebrush occur at 4,200-6,700 ft on slopes, ridgetops and benches. Toeslopes, terraces and alluvial fans at 3,800 ft to 5,300 ft, often with heavy soil, support shrublands dominated by big sagebrush (Artemisia tridentata), bird’s-foot sagebrush (Artemisia pedatifida), black greasewood (Sarcobatus vermiculatus), and Gardner’s saltbush (Atriplex gardneri). Idaho fescue grasslands occur above 8,000 ft on gentle slopes. Grasslands dominated by bluebunch wheatgrass and cushion plants are common on gravelly soils of low-elevation ridgetops and upper slopes.