Oak apple due to the superficial resemblance and the preponderance of the oak marble gall in the wild. Other galls found on oak trees include the oak artichoke gall and the acorn cup gall, but each of these has its own distinctive form. Some common oak-apple-forming species are the "Biorhiza pallida" gall wasp in Europe, "Amphibolips confluenta" in eastern North America, and "Atrusca bella" in western North America. Oak apples may be brownish, yellowish, greenish, pinkish, or reddish. Oak galls have been used in the production of ink since at least the time of the Roman Empire. From the Middle Ages to
Knights of the Royal Oak set aside as "Royal Oak Day," and "Oak Apple Day" to commemorate the Restoration. Celebration was made by the wearing of oak leaves in the hat; oak apples gilded, with a few leaves surrounding them, were sold in the streets of London. The statue of Charles I of England, at Charing Cross, was also decorated with branches of oak on this day. The holiday is still celebrated today as Oak Apple Day. Anglesey Brecknockshire Cardiganshire Carmarthenshire Caernarvonshire Denbighshire Flintshire Glamorganshire Merionethshire Monmouthshire Montgomeryshire Pembrokeshire Radnorshire Knights of the Royal Oak The Knights of the Royal Oak was an intended order