The Allegheny Plateau in the States of Pennsylvania and New York is an offshoot of the Appalachian Mountains. Its deciduous forests show features of the very species-rich forests that we find further south on the slopes of the Appalachian Mountains (arboretum Group 15). Various oak and maple species are found here mixed with linden, walnut, ash, and American beech, which differs from the European beech because of its larger and clearly serrated leaves. The Americans distinguish the white oaks with rounded leaf lobes, e.g. White oak and Swamp white oak, from the red oaks with pointed lobes, among which the imported Northern Red Oak and the Pin Oak are also well introduced in Europe. Red maple, Silver maple, and Sugar maple are the dominant maples; the smaller American Red snake bark maple with its olive-green bark and the Boxelder maple with its compound leaves are species of the understory, just like the American hornbeam and hazel. Pioneer species include the Eastern cottonwood, the Quacking aspen, the Yellow birch and the Sweet birch. An outsider is the Kentucky coffee tree, with its large bi-pinnate leaves during the summer and its bony appearance in winter.