North American Atlantic Region is a floristic region within the Holarctic Kingdom identified by Armen Takhtajan and Robert F. Thorne, spanning from the Atlantic and Gulf coasts to the Great Plains and comprising a major part of the United States and southeastern portions of Canada. It is bordered by the Circumboreal floristic region in the north, by the Rocky Mountain and Madrean floristic regions in the west and by the Caribbean floristic region of the Neotropical Kingdom in the south of Florida. The flora of the region comprises two endemic monotypic families, Hydrastidaceae and Leitneriaceae, and is characterized by about a hundred of endemic genera (such as Sanguinaria, Leavenworthia, Gillenia, Neviusia, Dionaea, Yeatesia, Pleea). The degree of species endemism is very high, many species are Tertiary relicts, which survived the Wisconsin glaciation and are now concentrated in the Appalachians (esp. Blue Ridge Mountains) and the Ozarks. A number of genera (Sarracenia, Uvularia etc.) are shared only with the Canadian floristic province of the Circumboreal region. Moreover, as has long been noted (e.g. by Joseph Gerhard Zuccarini and especially by Asa Gray), a large number of relict genera (Liriodendron, Hamamelis, Stewartia etc.) are shared with the relatively distant Eastern Asiatic Region (comprising Japan, Korea, and the east of China) and sometimes Southeast Asia. R. F. Thorne counted at least 74 genera restricted to eastern North America and Asia (mostly eastern and southeastern Asia). The fossil record indicates that during the Tertiary period a warm temperate zone extended across much of the Northern Hemisphere, linking America to Asia. Subdivisions The North American Atlantic Region is subdivided further into three floristic provinces: the Appalachian Province, Atlantic and Gulf Coastal Plain Province, and North American Prairies Province. L Appalachian Province The Appalachian Province comprises the upland eastern North America that was covered by deciduous forest in historic times, concentrated around the Appalachians and Ozarks, where its flora found refuge during Pleistocene glaciations. It stretches from southernmost Ontario and Quebec to Arkansas and easternmost Texas and from central Georgia and Alabama to eastern Iowa and southeastern Minnesota. The remaining wildland of the province is covered predominantly by temperate broadleaf and mixed forests dominated by oaks, hickories, maples and Tsuga and is characterized by the highest degree of endemism within the floristic region. It includes such ecoregions as the Appalachian mixed mesophytic forests, Appalachian-Blue Ridge forests and the Piedmont (as far east as the Fall Line).