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The nucleotide sequences of the nuclear ribosomal DNA including 18S, 5.8S, and 28S rDNA and the internal transcribed spacer regions were determined for 33 powdery mildew taxa spanning 15 genera to infer the phylogenetic relationships for these fungi. Phylogenetic analyses revealed that Uncinula septata was placed in the primitive base to the large clade composed of all other powdery mildew taxa. Powdery mildews excluding Unc. septata were split into five major lineages. The Pseudoidium lineage consisted of six genera, i.e., Erysiphe, Microsphaera, Uncinula, Uncinuliella, Brasiliomyces, and Typhulochaeta, all of which are characterized by polyascal cleistothecia and Pseudoidium-type anamorph. The Eudoidium lineage consisted of three Erysiphe species (E. cichoracearum, E. orontii and E. galeopsidis) and Arthrocladiella mougeotii, which are characterized by polyascal cleistothecia and Euoidium-type anamorph. The endophytic lineage consisted of two Phyllactinia species (Phy. moricola and Phy. Kakicola), Leveillula taurica and Pleochaeta shiraiana, which are characterized by the presence of endophytic or partly endophytic mycelia. The fibrosin lineage consisted of the genera Sawadaea, Cystotheca, Podosphaera, and Sphaerotheca, all of which are characterized by the presence of well-developed fibrosin bodies in the conidia and conidiophores. The monocot lineage consisted of a single species, Blumeria graminis, which is well characterized by being parasitic to monocots, especially to cereal plants. Character polarization was discussed on several major characteristics. The mycelioid appendage which has long been regarded as an ancestral character may be a derived character as a result of an event that may have occurred multiple times independently due to convergence. Euoidium-type anamorph and clavate appressorial germ tube are considered to be ancestral characters to Pseudoidium-type anamorph and lobed germ tube. Ectophytic nature and polyascal cleistothecia are also regarded as ancestral features to endophytic nature and monoascal cleistothecia.