Pseudomonas syringae is a rod-shaped, Gram-negative bacterium with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different pathovars, all of which are available to researchers from international culture collections such as the NCPPB, ICMP, and others. Whether these pathovars represent a single species is unclear. P. syringae is a member of the Pseudomonas genus, and based on 16S rRNA analysis, it has been placed in the P. syringae group. It is named after the lilac tree (Syringa vulgaris), from which it was first isolated.