This annual is widespread across most eastern states, except those adjacent to Canada. However, it is curiously absent to rare in some regions with a more deeply wooded history, including more rugged Appalachian hills and the calcareous region of c. Ky. and c. Tenn. Plants with longer awns have been named var. geniculata (Raf.) Fern., but may not deserve taxonomic recognition. There is little documented difference in range or habitat (FNA 25, W), although geniculata may extend further to the north and east (F). An initial study of DNA sequences indicated that typical longespica is distinct and closer to the perennial purpurascens (Cerros-Tlatilpa et al. 2011); but more thorough analysis of DNA, morphology and distribution is needed. There may be no clear vegetative differences from the associated annuals, oligantha and dichotoma; however, longespica tends to be more robust.