Stems often whitish pruinose, slender, to 6 mm diam., acrid-tasting; scales weakly bicolored, lanceolate, contorted distally, base and margins light brown, sometimes with dark central stripe, margins denticulate. Leaves to 40 cm. Petiole slender, to 2 mm diam. Blade oblong to narrowly lanceolate, pinnatifid, usually widest near middle, occasionally at or near base, to 7 cm wide, somewhat leathery; rachis sparsely scaly to glabrescent abaxially, glabrous adaxially; scales lanceolate-ovate, usually more than 6 cells wide. Segments oblong, less than 8 mm wide; margins entire to crenulate; apex rounded to broadly acute; midrib glabrous adaxially. Venation free. Sori midway between margin and midrib to nearly marginal, less than 3 mm diam., circular when immature. Sporangiasters present, usually less than 40 per sorus, heads covered with glandular hairs. Spores more than 52 µm, tuberculate, surface projections more than 3 µm tall. 2 n = 148. Sporulating summer--fall. Cliffs and rocky slopes; on a variety of substrates; 0--1800 m; St. Pierre and Miquelon; Alta., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask.; Ala., Ark., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., S.Dak., Tenn., Vt., Va., W.Va., Wis. Traditionally, two cytotypes have been recognized within Polypodium virginianum (I. Manton and M. Shivas 1953). Recent research has demonstrated that the tetraploid cytotype, which properly bears the name P . virginianum (R. Cranfill and D. M. Britton 1983), is an allopolyploid produced by hybridization between the diploid cytotype (here called P . appalachianum ) and P . sibiricum (C. H. Haufler and M. D. Windham 1991; C. H. Haufler and Wang Z. R. 1991). Although sometimes similar to its diploid parents in overall leaf morphology, P . virginianum has consistently larger spores, typically more than 52 µm (see additional comments under P . appalachianum and P . sibiricum ). Frequent hybridizations between P . virginianum and P . appalachianum form morphologically intermediate, triploid individuals with misshapen spores. Sterile triploids also result from hybridization between P . virginianum and P . sibiricum .
Rhizome 1.5-3 mm thick, the scales 2.5-5 mm, basally cordate, apically filiform-attenuate, entire, concolorous, light brown; lvs 8-40 cm, the petiole mostly 3-15 cm, scaly only at the very base; blade narrowly oblong, mostly 3-6 cm wide, narrowed to an acuminate tip, the rachis sparsely scaly beneath; segments mostly 12-20 pairs, 3-7 mm wide, slightly denticulate, apically obtuse, glabrous; veins evident, free, mostly twice-forked, terminating in hydathodes; sori superficial, borne close to the midvein of the segments, the sporangia intermingled with long glandular golden hairs; 2n=74, 111, 148. On rocks and banks in circumneutral soil, or seldom on tree-trunks; Nf. to Yukon, s. to Ga., Ala., Ark., and S.D. Perhaps equally well treated as var. virginianum (L.) D. C. Eaton of a broadly defined, circumboreal P. vulgare L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.