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).
Perennial fern 45 cm - 1.2 m tall Leaves: scattered, erect, evergreen (remain green even in winter), 30 - 75 cm long, 8 - 25 cm wide, oblong-lance-shaped in outline (widest just above base, tip abruptly long-pointed), but pinnately compound, herbaceous to papery, and mostly hairless except few multicellular hairs on "midrib" (rachis) and main veins. Rhizome: creeping, covered with brown, broadly lance-shaped scales. Leaf stalks: scattered along rhizome, erect, swollen at base, 15 - 50 cm long, with usually persistent scales at stalk base. Spores: 64 per sac, brownish, all of one kind, single-sectioned (monolete), oblong or kidney-shaped, and usually with a broad wing. The spores give rise to the gametophyte (the sexual phase of the plant), which is small, green, heart-shaped, hairless or often with glands or hairs, and sits above the ground.
Similar species: Diplazium pycnocarpon is probably most similar in appearance to Polystichum acrostichoides, but that species has leaf divisions (pinnae) with obvious ear-shaped lobes at the upper edge of their bases, the pinnae edges have spine-tipped teeth, the pinnae veins rarely fork more than once, and the round sori completely cover the entire lower surface of the pinnae. Some could confuse this species with robust plants of Asplenium platyneuron, but that species has shiny, very dark brown or purplish leaf stalks and "midribs" (rachis), usually shorter pinnae, and the base of the pinnae overlap the rachis.
Habitat and ecology: Rare, in undisturbed mesic woods, especially in Berrien County, Michigan.
Occurence in the Chicago region: native
Notes: This species has commonly been included in the genus Athyrium (as A. pycnocarpon), but research shows it is closely related to the east Malesian species Diplazium flavoviride (Kato 1993).
Author: The Field Museum
From Flora of Indiana (1940) by Charles C. Deam
Infrequent to frequent in southern Indiana, becoming less frequent to rare northward. It prefers deep humus and is most commonly found on the slopes of ravines in beech woods.