This is a cosmopolitan diploid (2n = 22) annual weed; efforts to distinguish segregates within the Western and Eastern Hemispheres have not been generally accepted (FNA 5). However, more northern and circumboreal plants treated as Polygonum scabrum Moench by F may deserve species status; these are unknown in Ky. The type of lapathifolium appears to be more like scabrum; there has been much confusion in herbaria and deeper revision is needed (R. Liesner, pers. comm.). See also notes under pensylvanica and bicornis; as in lapathifolium, those two species have ocreae with bristles lacking or < 1 mm, ocreolae mostly overlapping, achenes usually discoid, and leaves often with dark marks, at least in "var. prostratum" (Hobbs 1982)..