According to Roy Coombs, "Baroness de Rothschild" was a seeding of  Viola odorata  "Czar Bleu."  I keep hoping and watching and waiting, but I haven't found a seedling as elegant as this one.  The sweet blooms are large, blue/purple, and thoroughly recommended.    (de Rothschild, France, 1894)  Zones 4-9.