Clonal, with deep-seated long-creeping black rhizomes as well as erect leafy crowns; sterile lvs 0.5-2(-3) m, short-petiolate; blade ±hairy along the rachis and costae, oblanceolate, 1.5-5 dm wide, pinnae numerous, alternate, gradually reduced toward the base of the blade, more abruptly so upwards, long-acuminate, deeply pinnatifid with 20+ pairs of segments, these pinnately open-veined, oblong, obtuse, with slightly revolute, crenulate margin; fertile lvs produced from midsummer to early fall, not over 7 dm, the numerous pinnae 2-6 cm נ2-4 mm, obtuse, their numerous, crowded pinnules hooded; 2n=80. Swamps and moist woods in circumneutral soil; circumboreal, in Amer. s. to Va., Mo., S.D., and B.C. (M. pensylvanica; Pteretis nodulosa)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Varieties 2 (1 in the flora): North America, Eurasia.
From Flora of Indiana (1940) by Charles C. Deam
This species is, no doubt, very local in the state although it may have been overlooked because of its close resemblance to Osmunda cinnamomea. My specimens are mostly from alluvial flood plains of small streams.