This Eurasian annual is scattered across northeastern regions, but less common than helvetica (arvensis ssp. recta), which has been confused in some North American treatments (W, Y). Further checking of Ky. colls. is needed, but the few confirmed records of japonica date mostly from after 1980. It differs from helvetica in having an involucre of (3) 4-10 (12) bracts at the base of each umbel (versus 0-1 or occasionally 2); fruits tend to be smaller (averaging 2-3 mm long without bristles versus 3-4 mm), with bristles shorter (0.4-0.8 mm versus 0.6-1.1 mm), more ascending (versus nearly perpendicular) and less hooked; 2n = 16 (versus 12). Its leaves tend to have broader segments.