Athyrium filix-femina var. michauxii Mett.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Variety Description - Petiole commonly ca half as long as the blade, the basal scales often blackish; blade widest near the middle, the fourth or fifth pair of pinnae the largest; cilia of the indusia eglandular; spores yellowish to brownish. Nf. and Que. to Ont. and S.D., s. to Md., Va., Ky., and Mo. (A. angustum)