This northern species occurs in North America and East Asia. It is considered to be a "relict amphidiploid [2n=96] of the mixed mesophytic flora of the Lower Tertiary" that probably originated from hybridization of longifolia [2n=24] and arvensis [2n=72] (Tucker & Chambers 2002). Most or all colls. from Ky. are referable to var. glabrata Benth., but that taxon has not been generally recognized in recent treatments. Typical arvensis, a European taxon, may be naturalized in some northeastern regions (W), but reports from Ky. are probably based on canadensis (M). It differs from canadensis as follows (W): leaves subtending the inflorescence mostly broadly rounded at the base (versus mostly cuneate); leaves of the inflorescence relatively narrow. Further investigation is needed. Although canadensis (or "arvensis") is recorded from at least 15 counties, these plants may be declining across the state. There are almost no records dated fro after the 1980s; JC observed it in the wet meadow below visitor center at Big Bone Lick in 1997 (BOON). Records for the USA in iNaturalist.org suggest a rather abrupt boundary south of central Ind., southern Ohio and central W.Va,, except for scattered records along higher mountains down to the southern Appalachians of Tenn. and N.Car.