Phyllitis scolopendrium (L.) Newman
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Rhizome-scales lance-ovate, 5–6 × 1–2 mm, glabrous, iridescent; petiole 4–12 cm × 1–2 mm, sulcate above, densely scaly when young; blade to 35 × 4 cm, acute or acutish, cordate-auriculate at base, sparsely scaly beneath, especially along the midrib; sori to 2 cm; 2n=144. On limestone rocks and in sink-holes; rare and local; N.B., Bruce Peninsula of Ont., upper penins. of Mich., c. N.Y., and e. Tenn. and n. Ala. Our native plants are var. americana Fernald. The Eurasian var. scolopendrium, diploid (2n=72), somewhat larger, and differing in a number of minor details, is established here and there as an escape from cult.