This occurs mostly in midwestern to northeastern regions, generally on limestone clifftops. In Ky. it is known mostly from the Bluegrass and Knobs regions. It may be more frequent in western regions than records indicate; D mapped it across much of s. Ind. But see also notes under tenuiflorus, which has often been confused. Corollas vary much in degree of coloration across the range of this species; some plants in Ky. have distinct purple lines within the corolla. Both hirsutus and tenuiflorus differ from other eastern species in their relatively closed corolla throats, often with less distinct internal lines. Also, their stems usually have dense, long-curling, mostly glandular hairs (versus glabrous to canescent, but with non-glandular hairs except in inflorescences). Both species are perennials that spread with basal offsets; their growth rates, flowering behaviors and seed-germination ecologies are "very similar" (Clements et al. 1998).