5. Pellaea bridgesii Hooker, Sp. Fil. 2: 238, plate 142b. 1858.
Stems compact, ascending, stout, 5--10 mm diam.; scales mostly weakly bicolored, linear-subulate, 0.1--0.3 mm wide, centers dark brown, thin, margins lighter, thin, denticulate to entire. Leaves monomorphic, clustered on stem, 7--30 cm; croziers nearly glabrous. Petiole dark brown, lustrous, rounded adaxially, without prominent articulation lines. Blade linear, 1-pinnate, 1.5--4 cm wide; rachis brown throughout, straight, rounded adaxially, glabrous. Pinnae perpendicular to slightly ascending, usually not decurrent on rachis, simple and unlobed; costae absent. Ultimate segments broadly ovate to elliptic, 7--20 mm, leathery, glabrous; margins plane, not recurved, not covering abaxial surface, borders whitish, entire; apex obtuse to rounded. Veins of ultimate segments obscure. Sporangia sessile or subsessile, containing 64 spores, intermixed with abundant farina-producing glands. 2 n = 58.
Sporulating summer--fall. Rocky slopes and cliffs, on granitic substrates; 1200--3600 m; Calif., Idaho, Nev., Oreg.
The morphology of Pellaea bridgesii is so distinctive that its sectional (and even generic) placement in Pellaea has long been a source of contention. W. H. Wagner Jr. et al. (1983) documented the existence of sterile diploid hybrids (called P . × glaciogena ) between P . bridgesii and P . mucronata (see reticulogram), suggesting that P . bridgesii is most closely related to members of sect. Pellaea . In addition to the more obvious characters mentioned above, P . bridgesii is distinguished from other North American species (except P . ternifolia ) by its anastomosing veins.