A look through these keys to white Violets will help one understand what to look for, common species, etc. (Again, the future will bring a comprehensive post on this blog.):
Violets have many medicinal applications. Perhaps a good general idea to start with is that Violets nourish yin- they are moistening and cooling and address issues relating to the body's yin, the body fluids, and address issues of heat and inflammation.
Violets in TCM
Violets in "A Modern Herbal"