This annual is weedy and variable (2n = 40, 80), but largely restricted to east-central states (FNA 25, K). Like pectinacea, it may have been concentrated on banks of larger streams and rivers before becoming much more widespread after settlement. It has been confused with capillaris; see notes under that name. E. japonica (Thunb.) Trin. is a robust diploid (2n = 20) of warmer regions that can distinguished from the frankii and cilianensis groups by its glabrous, membranous ligules (versus ciliate). It is probably native to the Old World, but is locally frequent in riparian zones of the Gulf Coastal Plain, and has been found as far north as s. Ill. (FNA 25). It is expected in w. Ky.