Variation in this widespread North American species is complex and needs further study; there is a polyploid series (2n = 18 to 54) and many plants are apomictic (F, FNA 19, Y). Most colls. from Ky. are referable to the widespread weedy annual, var. strigosus. Several colls. appear transitional to E. annuus (see also under that name), but may be referable to the more northern E. strigosus var. septentrionalis (Fern.) & Wieg.) Fern. A few colls. from western counties (CALL at OKL, HICK at MUR, OHIO at KY) are referable to the more southern var. beyrichii (Fisch. & C.A. Mey.) Torr. & Gray ex Gray. Several Appalachian colls. (from CART, ELLI, JOHN, MCRE, WHIT) at least tend towards to var. discoidea Robbins. See also notes under E. allisonii.