Causing small to large, convex-concave, slightly swollen spots or blisters on leaves (occasionally deforming the whole leaf, but not forming true witches' brooms) on many species of Quercus.

Leaf spots start out as pale green to yellow and are slightly swollen, convex-concave blisters that vary in size. As the leaf matures, the spots become necrotic. A layer of asci form on the lower leaf surface (concave side). When fresh, the layer of asci resembles a palisade-like layer that is translucent-white and granular on the leaf surface. The fungus also can deform the entire leaf ...

Leaf blisters on an oak host, and the presence of naked asci characteristic of Taphrina sp. are good diagnostic characteristics for field and microscopic diagnosis. The fungus can be isolated on Potato dextrose agar or acidified PDA ... [see webpage for information needed for microscopy and chemical testing]