Quercus lusitanica
Quercus lusitanica, commonly known as gall oak, Lusitanian oak, or dyer's oak, is a species of oak native to Portugal, Spain and Morocco. Quercus lusitanica is the source of commercial nutgalls. These galls are produced by the infection from the insect Cynips gallae tinctoriae. They are used for dyeing.
Several other species are known colloquially as "gall oaks;" indeed, galls can be found on a large percentage of oak species. The specific epithet "lusitanica" refers to the ancient Roman Province of Lusitania, corresponding roughly to present-day Portugal and Extremadura in Spain.
