Mapping is provisional and incomplete. This species was described in 1989, and there has not yet been a thorough separation of records from typical obscurum (FNA 2, W). A few colls. appear to be somewhat intermediate; 2n = 68 in both species. L. hickeyi is distinguished by the lack of differentiation between its dorsal and ventral leaves versus lateral leaves. In obscurum, lateral leaves tend to be longer, twisted and more spreading, so that shoots tend to be wider (ca. 6-9 mm versus 3.5-7 mm). Also, lateral branchlets of hickeyi are terete (versus somewhat flattened). Its branches are generally ascending to inrolled and dense (versus spreading to horizontal and well separated). Both hickeyi and obscurum have northeastern ranges, but hickeyi extends into colder zones, and may be generally uncommon to rare in southern Appalachian regions. D. hickeyi can be expected in less mesic habitats than obscurum, but the ecological difference may be less than that between Diphasiastrum digitatum and D. tristachyum (J. Hickey, pers. comm.).