Erysiphe kissiana sp. nov.: First finding of sect. Californiomyces in Japan

•A new powdery mildew species was found on Castanopsis cuspidata.•This fungus was reported as Erysiphe kissiana sp. nov.•Morphological description and phylogenetic tree were provided.

A powdery mildew was found on Castanopsis cuspidata (Fagaceae) in November 2013. Morphological and molecular analyses revealed that this species is new to science belonging to Erysiphe sect. Californiomyces that is mainly distributed in tropical regions of Asia. Erysiphe kissiana sp. nov. is the first species of the section Californiomyces found in Japan. This species has also an affinity to E. gracilis and E. japonica both occurring on the Fagaceae, which suggests that these powdery mildews have speciated on hosts of the Fagaceae.