This cryptic taxon is closely related to apodum, and it has been combined or reduced to a subspecies in some treatments. It occurs mostly in regions around the Great Lakes, and it is also scattered through the Ozark region (FNA 2, Y). It is usually reported from calcareous substrates, where apodum is virtually absent. Although recently collected from ne. Tenn. (M. Brock, pers. comm.) and from Habersham Co., Ga. (P. Hyatt #11533 at GA), eclipes has generally not been recognized in southeastern states (W). In Ky. the only records are colls. from Eastview Barrens in HARD (KY), as identified by Cranfill (1980, 1991); and from "around cliff-face at base of waterfall" near Shanty Hollow Lake in WARR (ALBC, NCU), as identified by W.R. Buck. S. eclipes differs from apodum in its median leaves with long attentuate to bristled, veined and frequently recurved apices (versus acute to attentuate, usually keeled but with vein not extending almost to tip); lateral leaves tend to be smaller (ca. 1-2 x 0.5-1.3 mm versus 1.4-2.2 x 0.8-1.3 mm); its megaspores are usually larger, relatively shiny, and more coarsely reticulate (Buck 1977; Haines 2003).