Stems creeping; scales brown, broadly lanceolate, margins entire. Petiole 15--40(--50) cm. Blade oblong-lanceolate, 1-pinnate, 30--75 × 8--25 cm, ± narrowed to base with reduced proximal pinnae, broadest above base, abruptly acuminate to apex. Pinnae linear, ± entire to shallowly crenulate, base truncate or acroscopically auriculate, apex acuminate. Veins usually 1--2-forked, nearly reaching sinuses between crenations. Sori elongate, straight or slightly falcate, single or rarely double; indusia vaulted, ± thick. 2 n = 80. Moist woods and slopes in neutral soil; 150--1000 m; Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis. Diplazium pycnocarpon has commonly been placed in Athyrium , but it is closely related to the east Malesian Diplazium flavoviride Alston (M. Kato and D. Darnaedi 1988).
Rhizome ±creeping; lvs scattered, 6-11 dm, the blade longer than the petiole, 11-20 cm wide, gradually tapering above, only slightly reduced below, glabrous except for a few septate brown hairs on the rachis, costae, and veins; pinnae 20-30 pairs, subdimorphic, the fertile one slightly narrower than the sterile; sterile pinnae narrowly lance- linear, 7-12 cm נ10-13 mm, subsessile and rounded or subtruncate at the base, gradually tapering to the base, subentire or slightly toothed, the veins simple or forked, tending to run to the sinuses; indusia glabrous, narrow, elongate, straight or nearly so, following the anterior vein-branch and often reaching from near the costa to near the margin; 2n=80. Cool woods and talus slopes in circumneutral soil; s. Que. to Ont. and Minn., s. to Fla. and La. (Asplenium p.; Diplazium p.; Homalosorus p.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.