Phyllactinia guttata is a species of fungus in the Erysiphaceae family; 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.