This is a widespread species in calcareous regions of east-central states, but largely absent from more acid soils of the Appalachians and further east or north, Variation deserves further study. There is wide range of flower sizes, ca. 3-7 cm long and 2-4 cm wide (F, Y). A coll. from WAYN (KY) has creamy white flowers, and a pure white form was seen in HARR (Griffith Woods) during 2006. Also, the incidence of cleistogamy seems to vary widely in space and time.