Categorizing plant images at the variety level: Did you say fine-grained? - Julien Champ; Titouan Lorieul; Pierre Bonnet; Najate Maghnaoui; Christophe Sereno; Thierry Dessup; Jean-Michel Boursiquot; Laurent Audeguin; Thierry Lacombe; Alexis Joly (Pattern Recognit. Lett., 2016)