Cystopteris protrusa (Weath.) Blasdell
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Rhizome long-creeping, sparsely scaly but densely villous, the growing point produced 2-4 cm beyond the often more scattered lvs; petiole greenish or stramineous except often at the very base; minor axes of the blade with scattered glands; veins typically running into marginal teeth; lowermost pinnules mostly cuneate at the base, and often short-petiolulate; indusium ca 0.5 mm, usually entire; 2n=84; otherwise much like no. 1 [Cystopteris fragilis (L.) Bernh.]. Abundant in mesic woods; N.Y. and s. Ont. to s. Minn., s. to Ga., Ala., La., and e. Kans. (C. fragilis var. p.)