Osmunda regalis L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Lvs mostly 5–18 dm; petiole glabrous; blade bipinnate, broadly ovate, to 5.5 dm wide; pinnae 5–7 pairs, subopposite, the lowest slightly reduced; pinnules alternate, 7–10 to a side, oblong, to 7 × 2.3 cm, sessile or nearly so, rounded and oblique at the base, obtuse, serrulate, finely and closely veined; fertile pinnae borne at the ends of some of the blades, several pairs, the larger segments oblong, 6–11 × 2–3 mm, at first greenish, eventually brownish; 2n=44. Swamps and moist places, mostly in acid soil; circumboreal, in Amer. from Nf. to Sask., s. to Fla., Tex., and trop. Amer. Spring–early summer. The Amer. plant is var. spectabilis (Willd.) A. Gray.