Some ultimate segments (especially terminal segments) with hairlike scales abaxially near midrib; sporangia containing 64 spores; spores averaging 38--52 µm diam. 2 n = 58. Sporulating summer--fall. Cliffs and ledges, apparently confined to limestone; 100--300 m; Mo. This diploid taxon is currently known only from southeastern Missouri in the Ozark region, but a thorough survey of spore number per sporangium in Pellaea glabella from eastern North America may yield additional localities. Plants of P . glabella subsp. missouriensis occasionally hybridize with P . glabella subsp. glabella ; the hybrids are apogamous pentaploids resembling P . glabella subsp. glabella (G. J. Gastony 1988).