This may have originated in northern regions, especially from the Ohio Rv. to the Great Lakes, but it is now a widely scattered weed across North America (FNA 4). A. tuberculatus (perhaps including rudis) may have been widespread along larger rivers in Ky. before settlement; the first record appears to be from Short et al. (1833) as "Acnida cannabina L." The species has spread into cropped fields, but remains concentrated on lowlands, generally in damper soils than palmeri (Green & Martin 2015). It has become somewhat resistant to imazaquin, glyphosate and other herbicides, increasing its success in fields of corn and soybeans (Patton 2013, Chatham et al. 2015). Mapped records here include var. subnudus S. Wats., which is not recognized in recent treatments; see also notes under rudis, which is difficut to distinguish. A. cannabinus (L.) J.D. Sauer is a related species of Atlantic coastal marshes that was been reported from Ky. by BA in error (M). Some of these species in subgenus Acnida are not clearly distinguished by initial genomic analysis, with results from nuclear DNA indicating different relationships than results from chloroplast DNA (Waselkov et al. 2018); reported 2n = 32 in general, and there has probably been considerable hybridization.