Pellaea glabella subsp. occidentalis
Contr. Univ. Michigan Herb. 19: 39. 1993.
Ultimate segments glabrous; sporangia containing 64 spores; spores averaging 38–52 µm diam. 2n = 58.
Phenology: Sporulating summer–fall.
Habitat: Calcareous cliffs and ledges, usually on limestone
Elevation: 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.