Venus’ Pride or Large Houstonia [Houstonia purpurea], a member of the Madder (Rubiaceae) family, found on the Blue Ridge Parkway Shut-In Trail on 25 May 2013. The USDA website lists a North Carolina variety of this flower, Mountain Bluet, as endangered. An entry can be found in Newcomb’s Wildflower Guide, pages 158-159, for the Large Houstonia, and it says that it’s found in open woods and on slopes.
USDA Plants Listing: https://plants.usda.gov/home/plantProfile?symbol=HOPU2
This sign is at the entrance of the Shut-In trail near the N.C. Aborteum, just of State Highway 191, near mile post 393.7.