During a study of the species of Botryosphaeriaceaeassociated with oak decline in Tunisia, a large collection of Diplodiastrains were isolated from Quercus afares, Q. canariensisand Q. subertrees showing a progressive dieback of shoots and branches, trunk canker and exudates and collar rot. Most of the isolates were identified as Diplodia corticola, while two isolates from Q. canariensiswere morphologically and phylogenetically (ITS and tef1-α sequences data) distinct from all other known species of Diplodia. They are described here as Diplodia quercivorasp. nov. In addition, phylogenetic analyses showed for the first time the existence of two distinct lineages within D. corticola. In artificial inoculation experiments, D. quercivoracaused necrotic lesions on bark and wood of three Mediterranean oak species, Q. ilex, Q. pubescensand Q. suber. In particular, among the oak species tested, Q. pubescenswas the most susceptible.