This is widely scattered in eastern North America, except on most of the southeastern Coastal Plain. Rafinesque (1836, 1:31) expressed uncertainty about its naturalized versus native status, and this is still not resolved (W). In Ky. the plant tends to occur along trails or roads through woods, usually on medium-acid soils. Some plants in the state may be referable to C. vulgare var. neogaea (Fern.) C.F. Reed, which has been considered native to North America. F distinguished this taxon from the Eurasian var. vulgare as follows: flowers lilac-pink to white (versus purple-red); leaves larger (?), glabrous or only sparsely strigose on upper surfaces (versus copiously strigose-villous); and habit more upright (?). But in cooler zones of northeastern states, plants matching var. vulgare may be prevalent.