Some ultimate segments (especially terminal segments) with hairlike scales abaxially near midrib; most sporangia containing 32 spores; spores averaging 60--72 µm diam. n = 2 n = 116, apogamous.

Sporulating summer--fall. Calcareous cliffs and ledges, usually on limestone substrates; 0--1200 m; Ont., Que.; Ark., Conn., Ill., Ind., Iowa, Kans., Ky., Md., Mass., Mich., Minn., Mo., Nebr., N.Y., Ohio, Okla., Pa., Tenn., Tex., Vt., Va., W.Va., Wis.

G. J. Gastony (1988) has shown that this apogamous tetraploid was derived from Pellaea glabella subsp. missouriensis by an autopolyploid increase in chromosome number.

This species was not separated from the preceding species even in Britton and Brown, Illustrated Flora, edition 2, published in 1913. Pickett (Amer. Fern Jour. 4: 97-101. 1914) wrote an article entitled "A peculiar form of Pellaea atropurpurea Link" and set forth the differences at length, but he did not give it a name until in a later article (Amer. Fern Jour. 7: 3-5. 1917.) Butters (Amer. Fern Jour. 7: 77-87. 1917) took up the subject and listed the specimens at the Gray Herbarium to show the range of the two species. This species has the habitat of the preceding but it is less frequent. Pellaea atropurpurea is regarded as the southern representative of the genus in our area and has a mass distribution to the south of a line connecting Kansas and Connecticut. Pellaea glabella is regarded as the northern representative of the genus in our area and has its mass distribution north of that of Pellaea atropurpurea.