This is a widespread variable western and northern species; 2n = 36 and 54. In Ky. it occurs on several narrow limestone ridges in the eastern Knobs, together with other rare or disjunct species (e.g. Calamagrostis insperata). These populations are completely disjunct from the species' extension down the Ridge-and-Valley region to w. Va., and those in the Great Lakes region (PL, W). Var. laevigatus (Fern.) Blake of Pacific regions is widely cultivated, but is not known to have escaped in Ky. It has much larger fruit (ca. 12-20 mm versus 6-10 mm), less hairy leaves, and larger potential size (ca. 0.8-3 m versus 0.1-1 m tall).