The anamorphic state of a powdery mildew on trident maple (Acer buergerianum, Aceraceae), belonging to Sawadaea, has been observed since 1980 in Tokyo and other areas of Japan. Since the autumn of 2003, this fungus has begun to produce chasmothecia in various areas of Japan, which were consistent with Erysiphe nankinensis (= Uncinula nankinensis), but apparently contradictory to the characteristics of the anamorph. Based on a molecular phylogenetic analysis using DNA separately extracted from the anamorph and teleomorph of the fungus on A. buergerianum, it could be demonstrated that sequences of this fungus are sister to Sawadaea. As the anamorph belongs to Oidium subgen. Octagoidium and because of the phylogenetic position within the Sawadaea clade, the new combination Sawadaea nankinensis is proposed for this species. The genus Sawadaea is emended to comprise species with consistently unbranched appendages.

Sawadaea nankinensis comb. nov.: a powdery mildew fungus of Acer buergerianum Takam. [= Uncinula ljubarskii var. aduncoides (R.Y. Zheng & G.Q. Chen) R.Y. Zheng & G.Q. Chen], and E. nankinensis (F.L. Tai) U. Braun & S. Takam. (= U. nankinensis F.L. Tai), have been reported on A . buergerianum in China (Braun 1987;Chen et al. 1987). Erysiphe ljubarskii var. aduncoides was fi rst found in Japan in 2001 (Sugahara et al. 2005). Another powdery mildew has been reported on this plant since 1980 in Tokyo and other areas of Japan (Horie and Sugata 1985). Based on the morphological characteristics, this fungus has been considered an anamorph of the genus Sawadaea Miyabe. However, because this fungus did not produce any teleomorph, its accurate taxonomic position has been obscure for a long time. Since the autumn of 2003, this fungus has begun to produce chasmothecia in various areas of Japan. Morphological characteristics of the teleomorph were consistent with E. nankinensis, which was apparently contradictory to the characteristics of the anamorph. In this study, we conducted a molecular phylogenetic analysis using DNA separately extracted from anamorph and teleomorph of the fungus on A. buergerianum to elucidate its taxonomic position. Materials and methodsField observation, morphological studies, and samples examined Occurrence of powdery mildew of A. buergerianum was periodically observed from April to November 2006 at the campus of Mie University, Tsu, Japan (34°74.472′ N, 136°52.428′ E). Fresh collections of the powdery mildew fungus on A. buergerianum were examined by standard light microscopy (Axio Imager; Carl Zeiss, Göttingen, Germany) and differential-interference-contrast optical instruments and devices. The specimens examined are deposited at MUMH (Herbarium, Faculty of Bioresources,