sp. nov. (Erysiphaceae, Ascomycota), a powdery mildew species found on (Hydrangeaceae) with unusual appendages.

A powdery mildew (Erysiphales) has recently been collected on leaves of an ornamental shrub in Baihua Mountain, Beijing, China. Microscopic examination of the chasmothecia suggested a species belonging to Erysiphesect.Erysiphe, above all due to mycelioid chasmothecial appendages, although circinate apices of the appendages were rather in favour of Erysiphesect.Uncinula, which is a fairly rare combination of appendage characteristics in . Phylogenetic analyses of ITS and 28S rDNA sequences demonstrated that the two examined powdery mildew collections on clustered together as an independent lineage within with 100% bootstrap support, representing a species of its own, which is phylogenetically allied to, but clearly distinct from and, in addition, morphologically quite different from all known species on hosts belonging to the Hydrangeaceae. The new species on is described as .