Pellaea atropurpurea (Linnaeus) Link var. occidentalis E. E. Nelson, Fern Bull. 7: 30. 1899; P. glabella var. nana (Richardson) Cody; P. glabella var. occidentalis (E. E. Nelson) Butters; P. occidentalis (E. E. Nelson) Rydberg; P. pumila Rydberg

Ultimate segments glabrous; sporangia containing 64 spores; spores averaging 38--52 µm diam. 2 n = 58.

Sporulating summer--fall. Calcareous cliffs and ledges, usually on limestone; 500--2800 m; Man., Sask.; Mont., N.Dak., S.Dak., Utah, Wyo.

Most recent treatments refer to this taxon as Pellaea glabella var. occidentalis . It appears to be synonymous, however, with P . glabella var. nana , which was proposed 76 years earlier and has priority if the taxon is treated at varietal rank. This diploid (treated here as a subspecies) often shows prominent articulation lines near the base of the petiole, and plants with less divided leaves are occasionally misidentified as P . breweri . At least some of the sporangia of subsp. occidentalis are long-stalked, however, whereas those of P . breweri are sessile or subsessile.