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Madrean Region
The Madrean Region (named after the Sierra Madre Occidental) is a floristic region within the Holarctic Kingdom in North America, as delineated by Armen Takhtajan and Robert F. Thorne. It occupies arid or semiarid areas in the southwestern United States and northwestern Mexico and is bordered by the Rocky Mountain Region and North American Atlantic Region of the Holarctic Kingdom in the north and in the east, as well as by the Caribbean Region of the Neotropical Kingdom in the south.
The Madrean Region is characterized by a very distinct flora with at least three endemic families (Fouquieriaceae, Simmondsiaceae, and Setchellanthaceae). Crossosomataceae, Garryaceae, Lennoaceae, Limnanthaceae and Stegnospermataceae have their principal development here; for Onagraceae, Polemoniaceae and Hydrophyllaceae it is the major center of diversity. More than 250 genera and probably more than half of the species of the region are endemic to it according to Takhtajan.
==Floristic provinces==
The region is subdivided into four floristic provinces:
*Great Basin Province
*Californian Province
*Sonoran Province
*Mexican Highlands Province
=== Great Basin Province ===
The Great Basin Floristic Province includes most of the Great Basin, as well as the Colorado Plateau, the Snake River Plain, and Arizona north of the Mogollon Rim. It shares much of its flora with the neighboring provinces and has only a few endemic genera. Species endemism is also moderate (about 25%), but is much more considerable in such genera as ''Astragalus'', ''Eriogonum'', ''Penstemon'', ''Cymopterus'', ''Lomatium'', ''Cryptantha'', ''Chrysothamnus'', ''Erigeron'', ''Phacelia'', ''Castilleja'', and ''Gilia''.
The vegetation in the central Great Basin shrub steppe part of the province is dominated by ''Artemisia'' species and Chenopodiaceae genera. The Great Basin montane forests include ancient Great Basin Bristlecone Pine (''Pinus longaeva'') trees.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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