Does the parasite follow its host? Occurrence of morphologically barely distinguishable powdery mildew anamorphs on Oenothera spp. in different parts of the world

•Morphologically indistinguishable powdery mildews on Oenothera belonged to two species.•Erysiphe howeana and E. alphitoides infected Oenothera in different continents.•It remains unclear how E. howeana spread quickly from one continent to another.•This is the first report of the tree-parasitic E. alphitoides on herbaceous plants.

To identify powdery mildew fungi infecting Oenothera spp. in Europe, specimens collected worldwide were examined based on morphology and internal transcribed spacer (ITS) sequences of the nuclear rRNA gene complex. The specimens were morphologically barely distinguishable from each other, each exhibiting pseudoidium-type conidiophores but sexual morphs lacking. Surprisingly, based on ITS sequence analyses, these specimens represented two species, i.e. Erysiphe howeana, known to infect Oenothera spp., and Erysiphe cf. alphitoides, which has never been recorded on herbaceous plants. Both species were detected on the invasive O. biennis in different parts of the world including regions where O. biennis was introduced only recently.