Phyllactinia guttata is a species of fungus in the family Erysiphaceae; the anamorph of this species is Ovulariopsis moricola. A plant pathogen distributed in temperate regions, P. guttata causes a powdery mildew on leaves and stems on a broad range of host plants; many records of infection are from Corylus species, like filbert (Corylus maxima) and hazel (Corylus avellana). Once thought to be conspecific with Phyllactinia chorisiae, a 1997 study proved that they are in fact separate species.

Microscopically, P. guttata is characterized by large ascomata, long narrow pointed appendages with bulbous swellings at base, 2- or 3-spored asci with large ascospores; the ascomata also have gelatinous cells with tufts of hyphae somewhat resembling hairs. The cleistothecia are capable of dissemination and attachment to new growing surfaces by means of gelatinous penicillate cells.

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