The northernmost plant pathogenic fungus, Rhytisma arcticum sp. nov.: Morphological and molecular characterization of a novel species from Ellesmere Island, Canada

Abstract A novel fungal pathogen, Rhytisma arcticum , is described, causing tar spot disease on Salix arctica in Ellesmere Island, Canada. Stromata, asci and ascospores—distinctly smaller than other Rhytisma species found on Salix —are its distinctive morphological features. rDNA internal transcribed spacer (ITS) and large‐subunit (LSU) sequence analyses revealed a close relation of this species to R. polare previously reported on Spitsbergen Island. This study describes a novel plant pathogen species in one of the northernmost locations of the world.