This is a widespread northeastern species with variation that needs further study. It mostly occurs in two distinct habitats: calcareous cliffs (especially to the west), and on sandstone boulders along Appalachian rivers. Var. intermedius (Rydb.) B.L. Robins. has distinctly stellate-pubescent fruits (follicles), and may deserve species status (W; FNA, in prep.). It has a largely midwestern range, was recently found in w. Tenn. (D. Estes, pers. comm.), and probably occurs in Ky.