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Taxonomic Summary. In order to count the number of unique biological entities in the flora, a species was counted if it consists only of a binomial or if it has a single trinomial in the study area. If the species consists of two or more subspecies or varieties, the first was counted as a species, and subsequent ones as subspecies or varieties. For example, Sambucus racemosa L. which consists, in our area, of var. melanocarpa (A. Gray) McMinn and var. microbotrys (Rydb.) K. & P. adds one to the species count and one to the variety count. The total number of unique biological entities is 2479, the sum of 2255 species, 12 hybrid species, 40 subspecies, and 169 varieties. The number of unique entities for major groups are as follows: Ferns (35 species in 7 families); “Fern Allies” (11 species in 4 families); Gymnosperms (22 species and 1 variety in 3 families); and Angiosperms (2191 species, 12 hybrid species, 40 subspecies, and 168 varieties in 108 families, counting the subfamilies of Fabaceae as families).

            Given that the study area is 65,382 km² (25,244 square miles), the density of unique biological entities is 1 per 26.4 km² (10.2 mi²). As a comparison, the density of unique entities in Colorado (270,000 km², 104,247 mi²; Hartman & Nelson, 2002) is 1 per 78.7 km² (30.39 mi²) and Utah (219,932 km², 84,916 mi²; Welsh et al., 1993) is 1 per 59.8 km² (23.09 mi²). Counts of unique entities are not available for Arizona and New Mexico.