[Page 1] Erysiphe aquilegiae DC. is a common powdery mildew infecting the Ranunculaceae. In his monograph of the Erysiphales, Braun (1987) accepted two varieties of this species, Erysiphe aquilegiae var. aquilegiae and Erysiphe aquilegiae var. ranunculi (Grev.) Zheng & Chen. These two taxa were differentiated by their cleistothecial appendages. Those of E. aquilegiae var. ranunculi are 0.5-4 times the diameter of the cleistothecia and mycelioid, while those of E. aquilegiae var. aquilegiae are (1)3-12 times the diam of the cleistothecia and straighter. [Page 7] The lack of any ITS sequence difference between E. aquilegiae var. aquilegiae and E. aquilegiae var. ranunculi (with the exception of the material on Delphinium) was unexpected, but may indicate how very recently these two taxa diverged. In this respect, Boesewinkel’s (1979) decision to accept only a single species and Braun’s (1987) decision to retain the two taxa as varieties of one species seems to be justified by their genetic similarity (at least in the ITS region).