A virus isolate from Pelargonium spp., provisionally designated UPEV (unknown pelargonium virus), had isometric particles 31-33 nm in diameter, with a granular surface structure similar to that of viruses in three genera of family Tombusviridae. Immunoelectron microscopy proved that UPEV was serologically distinct from all examined morphologically similar members of the family Tombusviridae. The induced cytopathology was characterized by large cytoplasmic virion aggregates and the formation of multivesicular bodies derived from mitochondria. Analysis of the complete ssRNA genome sequence revealed four open reading frames (ORFs) arranged like those of viruses in the genera Tombusvirus and Aureusvirus. Sequence comparisons indicated that three of the four ORFs had a high identity (52-97% identical amino acids) with the respective ORFs of tombusvirus species, especially with Carnation Italian ringspot virus, but not with those of viruses in other genera in Tombusviridae. On the contrary, UPEV coat protein had a low indentity (36-53% identical amino acids) with that of the aureusvirus Pothos latent virus. The data suggested that UPEV originated in a recombination event between a tombus- and an aureusvirus. According to its original host and symptom expression we proposed the new virus be named Pelargonium necrotic spot virus (PeNSV) and classified it as a distinct and new species in the genus Tombusvirus.