This widespread perennial weed has probably been present since early after settlement (Short et al. 1933). Most or all plants in Ky. are referable to var. agrestis (Wallr.) DC., but that taxon has generally not been recognized in recent treatments. A. arvensis has often been misidentified as cotula, and some records need to be rechecked. BA's report of A. tinctoria L. was based on misidentified arvensis (M). A. arvensis differs from cotula as follows (FNA 19, W): rays fertile and pistillate (versus sterile and usually neutral) ;receptacle chaffy throughout (versus only toward the middle); involucres 6-13 mm (versus 5-9 mm). Also, plants are "not notably scented" nor clearly glandular (versus "usually ill-scented" and gland-dotted); stems are decumbent to erect, with branches mostly proximal (versus usually erect, with branches mostly distal or throughout); and leaves tend to be smaller (15-35 x 8-16 mm versus 25-55 x 15-30 mm). Seeds tend to be larger (see also https/inspection.canada.ca): mostly1.7-2.8 x 1-1.5 mm (versus 1-2.3 x 0.8-1 mm) and smooth or weakly tuberculate (versus strongly tuberculate).