[Ophioglossum pycnostichum (Fern.) Löve & Löve, moreOphioglossum vulgatum var. alaskanum (E. G. Britt.) C. Chr., Ophioglossum vulgatum var. pycnostichum Fern.]
Blade widest below the middle, more abruptly rounded to the base, dark green, firm; basal sheath leathery and ±persistent; spores avg 35-45 microns; low woods and flood plains, southern, mostly s. of the glacial boundary, s. to Fla. and Mex. (O. pycnostichum)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.