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, 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 Tertiar