Icon. Filic. 1: 56. 1829.
Stems conspicuously whitish pruinose, stout, 3–12 mm diam., bland to slightly sweet-tasting; scales concolored to weakly bicolored, uniformly dark brown or with pale margins and base, lanceolate, symmetric, margins denticulate. Leaves to 85 cm. Petiole stout, to 3 mm diam. Blade ovate-lanceolate, pinnatifid, usually widest just above base, to 27 cm wide, stiff and leathery; rachis sparsely scaly to glabrescent abaxially, glabrous adaxially; scales bicolored, ovate-lanceolate, much more than 6 cells wide. Segments oblong to linear, usually more than 12 mm wide; margins entire to crenulate; apex rounded to rarely broadly acute; midrib glabrous adaxially. Venation anastomosing, usually forming 1 row of areoles. Sori crowded against midrib, usually more than 3 mm diam., circular when immature. Sporangiasters absent. Spores usually less than 52 µm, rugose, surface projections less than 3 µm tall. 2n = 74, 111.
Phenology: Sporulating late fall–spring.
Habitat: Cracks and ledges on cliffs, occasionally epiphytic, on a variety of substrates but preferring volcanic substrates in warmer, drier climates, rarely far from ocean
Elevation: 0–500 m
B.C., Calif., Oreg., Wash., Mexico in Baja California.
The distinctive Polypodium scouleri has occasionally been assigned to the genus Goniophlebium because of its anastomosing venation and conspicuous areoles. Its venation pattern can be quite variable, however, and cannot be used as the sole feature distinguishing P. scouleri from P. californicum. Combining venation characteristics with others provided in the key distinguishes it clearly from its congeners in Polypodium. Some evidence suggests that P. scouleri hybridizes with P. californicum (S. A. Whitmore, unpubl.). I. Manton (1951) reported diploid and triploid cytotypes for P. scouleri, and variation in spore size suggests that the species may also include tetraploid populations.