Lastrea thelypteris (Linnaeus) Bory var. pubescens Lawson, Edinburgh New Philos. J., n.s. 19: 277. 1864; Dryopteris thelypteris (Linnaeus) A. Gray var. pubescens (Lawson) Weatherby; Thelypteris palustris var. haleana Fernald

Stems long-creeping, 1--3 mm diam. Leaves monomorphic or slightly dimorphic, dying back in winter, often 1--3 cm apart, fertile leaves more erect, narrower, and with somewhat contracted pinnae and segments, 20--90 cm. Petiole straw-colored above base, 9--45(--60) cm × 1--3 mm, at base sparsely set with tan, ovate, glabrous scales. Blade lanceolate, 10--40(--55) cm, proximal pinnae commonly slightly shorter, blade tapering gradually to pinnatifid apex. Pinnae pinnatifid to within 1 mm of costa, 2--10 × 0.5--2 cm; segments oblong, somewhat oblique, entire; proximal pair of veins from adjacent segments meeting margin above sinus, veins frequently forked. Indument abaxially of sparsely to densely set hairs on costae and sometimes veins, costae also commonly with a few small, tan scales, blade tissue glabrous on both sides. Sori round, medial; indusia tan, often hairy; sporangia glabrous. 2 n = 70.

Terrestrial in swamps, bogs, and marshes, also along riverbanks and roadside ditches, and in wet woods; 0--1000 m; St. Pierre and Miquelon; Man., N.B., Nfld., N.S., Ont., P.E.I., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis.; perhaps Mexico (as Dryopteris tremula H. Christ); West Indies in Bermuda, Cuba.