Leaves monomorphic, dying back in winter, 28--120 × 10--30 cm. Petiole less than 1/4 length of leaf, scaly at least at base; scales scattered, brown, of 2 distinct kinds, 1 broad, 1 hairlike (only this species has 2 distinct forms of scales without intermediates). Blade green, ovate-lanceolate, pinnate-pinnatifid to 2-pinnate at base, firm but not leathery, not glandular. Pinnae ± in plane of blade, lanceolate; basal pinnae ovate-lanceolate, much reduced, basal pinnules or segments ± same length as adjacent pinnules, basal basiscopic pinnule and basal acroscopic pinnule equal; pinnule margins serrate to lobed. Sori midway between midvein and margin of segments. Indusia lacking glands. 2 n = 164. Dense woods and talus slopes on limestone (ne North America); open woods among boulders and talus of granite or igneous rock (Rocky Mountains); 200--2500 m; Greenland; Alta., B.C., Nfld., N.S., Ont., Que., Sask.; Ariz., Calif., Colo., Idaho, Mich., Mont., N.Mex., Nev., Okla., Oreg., Tex., Utah, Wash., Wis., Wyo.; Europe; Asia. The taxonomy of Dryopteris filix-mas is not well understood. In North America, this fern has been considered both an auto- and an allopolyploid and may be composed of at least two closely related taxa. Plants in the northeast and northwest are tetraploid. These differ morphologically and ecologically from a taxon of unknown chromosome number in the southwestern Rocky Mountains. The Rocky Mountain taxon closely resembles the Mexican D . pseudofilix-mas (Fée) Rothmaler. Dryopteris filix-mas also occurs in Europe, and it is known to be an allopolyploid of D . caucasica (A. Braun) Fraser-Jenkins & Corley × oreades Fomin.

Rhizome ascending or erect; lvs mostly deciduous, appearing more delicate and finely divided than in spp. 5 and 6; petiole a third as long as the blade, its numerous scales pale, concolored, the broad, toothed ones intermingled with narrow, hair-like ones; blade to 10+ dm, mostly 1.5-3 dm wide; pinnate-pinnatifid with numerous (mostly 20-30 pairs) of pinnae to 15 נ4 cm, the largest pinnae near or a little below the middle and with (15)20+ pairs of segments, many of the segments evidently contracted at the base; larger ultimate segments (0.7-)1-1.5(-2) cm; ramentum ±plentiful on the rachis and costae, sometimes on the lower surface of the blade, chiefly of narrow, elongate, hair-like scales, that of the rachis sometimes partly of more evident (but still narrow) scales; 2n=164. Thickets, moist woods, and streambanks; circumboreal, extending s. to Vt., n. Mich., ne. Ill., S.D., and Mex.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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