Oaks are host to majority of galls but other trees and shrubs affected as well.
Galls of certain inciters have a distinctive shape, occupy specific sites such as leaves, twigs and bark, and locations thereon, such as o the top or bottom of leaves, on veins, interveinal, at leaf margins and on petioles. They are unique to a specific host genus. Oak trees serve as host to a clear majority of all known and classified galls. Galls are more of an aesthetic nature than an acute detriment to overall tree health. People first become aware of galls only after they have developed.