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Remarks (public):For a complete description including images see 
Remarks (internal):Not uncommon on hard wood trea but rarely causing damage.
Description type:Non-original description 
Description:Phyllactinia guttata (Wallr.: Fr ) Lév., Ann. Sci. nat. III. 15: 144, 1851.
= Erysiphe betulae DC., 1815.
= Elysiphe alni DC., 1815.
= Alphitomorpha guttata Wallr., 1819.
= Erysiphe guttata Fr., 1829.
= Phyllactinia suffulta (Rabenh.) Sacc., 1882.
= Phyllactinia corylea (Pers.) Karst. em. Salm., 1900.
Mycelium hypophyllous, often evanescent but sometimes more or less persistent, rarely forming definite patches. Conidia borne singly, dub shaped or roughly rhomboid in outline, about 50-90 x 10-20 µm. Cleistothecia usually scattered but sometimes gregarious, globose-depressed, 160-230 µm diam. (mostly under 200 µm), cells rather indistinct; apex of ascocarp provided with a mass of densely crowded penicillate cells which are special outgrowths from the external cells each terminating in a fascicled head of numerous short hyphal branches. Appendages 6-15, equatorially inserted, 1-1½ times as long as the diameter of the ascocarp, hyaline to subhyaline, rigid, acicular, straight, aseptate; swollen at the base into a hollow bulb. Asci 8-25, subcylindric to ovate-oblong, 70-100 x 25-40 µm. Ascospores 2 rarely 3, variable in size and shape, 25-45 x 15-25 µm. Distinguished from other species of Phyllactinia mainly by the size of the cleistothecia (160-230 µm).
Hosts: On numerous woody plants, chiefly Betulaceae (Betula, Carpinus, Corylus, Ostrya), Fagaceae (Castanea, Fagus, Quercus) and Juglandaceae (Juplans, Platyearya, Pterocarya). Also on Acer, Aesculus, Aralia, Asclepias, Azalea, Buxus, Catalpa, Chionanthus, Cornus, Frangula, Hedera, Humulus, Paliurus, Populus, Prunus, Rhamnus, Ribes, Salix, Sorbus, Syrinpa, Ulmus (Blumer, 1967; Hirata, 1966).
Disease: Powdery mildew of hard wood trees induding hazel, birch, hornbeam, alder.
Geographical distribution: Asia (China, Fonnosa, India, Iran, Japan, Korea, Turkey, U.S.S.R.); Europe (widely distributed); Canada; U.S.A. (Hirata, 1966).
Physiological specialization: The following biologic forms are known: f.sp. carpini; f.sp. coryli; f.sp. Betulae; f.sp. fagi; f.sp. alzu (Blumer, 1967).
Transmission: Cleistothecia are capable of dissemination and attachment to the new substratum by means of penicillate cells.
Literature: Blumer, Beitr.Krypt. Fl. Schweiz 7(1): 391-396, 1933; Blumer, Echte Mehltaupilze, pp. 317-320, 1967; Junell, Trans. Br. mycol. Soc. 48: 546, 1965; Salmon, Mem. Torrey bot. Club 9: 224-236, 1900 (taxonomy and general account); Hirata, Host range and geographical distribution of the powdery mildews, Japan: Niigata Univ. 1966.

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