The powdery mildew Erysiphe magnifica (Erysiphales, Ascomycota) has been recorded for the first time on lotus (Nelumbo nucifera) based on a collection from the Botanical Garden in Frankfurt am Main, Germany. This powdery mildew previously known only from Magnolia species was identified by a combination of light and scanning electron microscopic investigation of ascomata and the Oidium stage, and comparison of ITS DNA sequences. This finding is discussed with respect to the narrow host specificity concept used in Erysiphales taxonomy, the effect of lotus leaf surface on fungal infection, and the extending geographical distribution of powdery mildews.