Wildflowers of the Blue Ridge Parkway
J. Anthony Alderman
Not just a field guide, but a tour guide to 75 of the best sites along the Parkway for viewing wildflowers in spring, summer, and fall.
University of North Carolina.
This book is out of print, but still useful! Check out your local used bookstores or an online source like AbeBooks.
To select from a dropdown list of genera, type only the first 2-3 letters.
If "briar" doesn't deliver the results you want, try an alternate spelling such as "brier", etc.