9. Polypodium virginianum Linnaeus, Sp. Pl. 2: 1085. 1753.
Rock polypody, tripes-de-roches, polypode de virginie
Polypodium vinlandicum A. Löve & D. Löve; P. vulgare Linnaeus var. americanum Hooker; P. vulgare var. virginianum (Linnaeus) D. C. Eaton
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 .