Ultimate segments essentially glabrous; 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; 900--3000 m; Alta., B.C.; Ariz., Colo., Idaho, Mont., N.Mex., Utah, Wash., Wyo. This western counterpart of Pellaea glabella subsp. glabella is an apogamous tetraploid. A. F. Tryon (1957) and D. B. Lellinger (1985) hypothesized that it might have arisen as a hybrid between the western diploid member of the P . glabella complex (here called subsp. occidentalis ) and P . atropurpurea . G. J. Gastony (1988) has shown conclusively, however, that P . glabella subsp. simplex is an autopolyploid derivative of subsp. occidentalis and does not contain genes contributed by P . atropurpurea .