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. 2n = 80.
Habitat: Moist woods and slopes in neutral soil
Elevation: 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).