Ophioglossum engelmannii Prantl
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Bases of old lvs persisting on the rhizomes; lvs often 2 or more, the blade usually somewhat trough-shaped in life, acute at each end, apiculate, the veins forming areoles that enclose many smaller areoles and also some free veinlets; otherwise much like O. vulgatum. Woods, pastures, and ledges, mostly in calcareous soils; nw. Va. to s. Ill. and e. Kans., s. to Fla., Ariz., and Mex. Spr.–early summer.