Petiole 13--55 cm; scales light brown or brown, lanceolate, 6--9 × 2 mm, ± crisped. Blade ovate-lanceolate to lanceolate, 2-pinnate-pinnatifid, (18--)25--60 × (5--)10--30 cm, slightly narrowed proximally, broadest just above base to just below middle, apex acuminate or ± caudate. Pinnae usually stalked, oblong-lanceolate to lanceolate, base truncate, apex acuminate. Pinnules oblong-lanceolate to narrowly deltate, base unequally cuneate, apex ± acute. Rachis , costae, and costules glabrous or with scales or pale glands. Sori elongate, straight or hooked at distal end or horseshoe-shaped; sporangial stalks with glandular hairs; indusia ciliate, hairs glandular or nonglandular and ± as long as indusial width. Spores brown or dark brown. 2 n = 80. Moist woods, thickets, swamps; 10--2000 m; Ala., Ark., Conn., Del., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Mass., Miss., Mo., N.J., N.Y., N.C., Okla., Pa., R.I., S.C., Tenn., Tex., Va., W.Va.
Petiole nearly or fully as long as the blade, the basal scales pale; blade widest below the middle, the second or third pair of pinnae the largest; cilia of the indusium gland- tipped; spores dark brown or blackish. Fla. to e. Tex., n. to R.I., Pa., s. Ind., Mo., Okla., and e. Kans. (A. asplenioides)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.