This annual appears to have originally been centered in the Mississippi Valley, but became widely adventive in Appalachian and Atlantic regions (F, Cr, W). Although probably increased since Gm's time, aristata remains much more common in western regions of the state. Some hybridization may be expected with patagonica (Cr); 2n = 20 in both. Section Gnaphaloides also includes P, ovata Forssk. (2n = 16), which originates from the Mediterranean regon and is widely cultivated as the source of "psyllium seed"; it is naturalized in the southwestern U.S.A. (K).