This perennial occurs mostly in subxeric woods of midwestern regions, usually with frequent Quercus alba and Q. rubra on somewhat base-rich soils. In Ky. its range is somewhat fragmented, and in Tenn. the species is rare. Its closest relatives may be G. palustre L. and G. asprellum Michx., which are more northern species of damp or wet habitats, often also on somewhat base-rch soils; they are known from W.Va., Va. and e. Tenn. but not Ky. (K). G. palustre differs from concinnum as follows (W): leaves rounded, obtuse, or barely acute (versus sharply acute or cuspidate); corolla ca. 4 mm across (versus 2.5-3 mm). G. asprellum differs from conconnum and palustre as follows (W): leaf margins retrorsely ciliate-scabrid (versus antrorsely); leaves with L/W = 3-5 (versus 4-8).