The Madrean region (named after the

Sierra Madre Occidental The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through northwestern and western Mexico, and along the Gulf of California. The Sierra Madre is part of the American C ...

) is a

floristic region A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both re ...

within the Holarctic kingdom in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, as delineated by

Armen Takhtajan Armen Leonovich Takhtajan or Takhtajian (; surname also transliterated Takhtadjan, Takhtadzhi︠a︡n or Takhtadzhian, pronounced takh-tuh-JAHN; 10 June 1910 – 13 November 2009), was a Soviet- Armenian botanist, one of the most important fi ...

and Robert F. Thorne. It occupies arid or semiarid areas in the southwestern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

and northwestern

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

and is bordered by the Rocky Mountain floristic region and North American Atlantic region of the Holarctic kingdom in the north and in the east, Caribbean region of the Neotropical kingdom in the south. The Madrean region is characterized by a very distinct

flora Flora (: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. The corresponding term for animals is ''fauna'', and for f ...

with at least three

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

(

Fouquieriaceae ''Fouquieria'' is a genus of 11 species of desert flowering plants, the sole genus in the family Fouquieriaceae. The genus is native to North America and includes the ocotillo ('' F. splendens'') and the Boojum tree or cirio ('' F. columnaris''). ...

Simmondsiaceae Simmondsiaceae or the jojoba family is a family of flowering plants. The family is not recognized by all taxonomic systems, the single species, '' Simmondsia chinensis'', often being treated as belonging to family Buxaceae. The APG II system, o ...

, and

Setchellanthaceae ''Setchellanthus caeruleus'' is a species of pungent shrub with large blue flowers. It is placed alone in the genus ''Setchellanthus'', which is in turn, is placed alone in the family Setchellanthaceae. It is endemic to Mexico. The genus and the ...

Crossosomataceae Crossosomataceae is a small plant family, consisting of four genera of shrubs found only in the dry parts of the American southwest and Mexico. This family has included up to ten species in the past, although as of 2021 six species are still rec ...

Garryaceae Garryaceae is a small family of plants known commonly as the silktassels.Garryaceae.
Flora ...

Lennoaceae Lennooideae is a subfamily of parasitic flowering plants of southwestern North America and northwestern South America. The relationships of this subfamily to other plants remain uncertain. It was traditionally treated at family rank as Lennoacea ...

Limnanthaceae The Limnanthaceae are a small family of annual herbs occurring throughout temperate North America. There are eight species and nineteen taxa currently recognized. Members of this family are prominent in vernal pool communities of California. Some ...

and

Stegnospermataceae ''Stegnosperma'' is a genus of flowering plants, consisting of three species of woody plants, native to the Caribbean, Central America, and the Sonoran Desert. These are shrubs or lianas, with anomalous secondary thickening in mature stems, by su ...

have their principal development here; for

Onagraceae The Onagraceae are a family of flowering plants known as the willowherb family or evening primrose family. They include about 650 species of herbs, shrubs, and trees Polemoniaceae The Polemoniaceae (Jacob's-ladder or phlox family) are a family of flowering plants consisting of about 27 genera with 270–400 species of annuals and perennials native to the Northern Hemisphere and South America, with the center of diversity ...

and Hydrophyllaceae it is the major center of diversity. More than 250

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

and probably more than half of the

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of the region are

to it according to Takhtajan.

Floristic provinces

The region is subdivided into four

floristic provinces A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both re ...

: * Great Basin province * Californian province *Sonoran province * Mexican Highlands province

Great Basin province

The Great Basin floristic province includes most of the

Great Basin The Great Basin () is the largest area of contiguous endorheic watersheds, those with no outlets to the ocean, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja Californi ...

, as well as the

Colorado Plateau The Colorado Plateau is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the Southwestern United States. This plateau covers an area of 336,700 km2 (130,000 mi2) within w ...

, the

Snake River Plain The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges, gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geology, geologic feature located primarily within the U.S. state of Idaho. ...

, and Arizona north of the

Mogollon Rim The Mogollon Rim ( or or ) is a topography, topographical and geological feature cutting across Northern Arizona, the northern half of the U.S. state of Arizona. It extends approximately , starting in northern Yavapai County, Arizona, Yavapa ...

. It shares much of its flora with the neighboring provinces and has only a few endemic

Species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

endemism is also moderate (about 25%), but is much more considerable in such genera as ''

Astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

'', ''

Eriogonum ''Eriogonum'' is a genus of flowering plants in the family Polygonaceae. The genus is found in North America and is known as wild buckwheat. This is a highly species-rich genus, and indications are that active speciation is continuing. It incl ...

'', ''

Penstemon ''Penstemon'' , the beardtongues, is a large genus of roughly 280 species of flowering plants native to North America from northern Canada to Central America. It is the largest genus of flowering plants endemic to North America. As well as bein ...

'', '' Cymopterus'', ''

Lomatium ''Lomatium'' is a genus in the family Apiaceae. It consists of about 100 species. Its common names include biscuitroot, Indian parsley, and desert parsley. It is in the family Apiaceae and therefore related to many familiar edible species such a ...

'', ''

Cryptantha ''Cryptantha'' is a genus of flowering plants in the borage family, Boraginaceae. They are known commonly as cat's eyes and popcorn flowers (the latter name is also used to refer to the Affinity (taxonomy), closely related genus ''Plagiobothrys' ...

'', ''

Chrysothamnus ''Chrysothamnus'', known as rabbitbrush, rabbitbush, and chamisa, are a genus of shrubs in the family Asteraceae. The native distribution is in the arid western United States, Canada, and northern Mexico. It is known for its bright white or yell ...

'', ''

Erigeron ''Erigeron'' () is a large genus of plants in the composite family (Asteraceae). It is placed in the tribe Astereae and is closely related to the Old World asters (''Aster (genus), Aster'') and the true daisies (''Bellis''). The genus has a cosm ...

'', ''

Phacelia ''Phacelia'' (phacelia, scorpionweed, Heliotropium, heliotrope) is a genus of about 200 species of annual plant, annual or perennial plant, perennial herbaceous plant, herbaceous flowering plant, plants in the borage family, native to North Ameri ...

'', ''

Castilleja ''Castilleja'', commonly known as paintbrush, Indian paintbrush, or prairie-fire, is a genus of about 200 species of Annual plant, annual and Perennial plant, perennial mostly herbaceous plants native to the west of the Americas from Alaska sout ...

'', and ''

Gilia ''Gilia'' is a genus of flowering plants in the Polemoniaceae family and is related to phlox. It includes 39 species native to the Americas, ranging from British Columbia to Texas and northern Mexico, and to Ohio, in North America, and from Ecua ...

''. The vegetation in the central Great Basin shrub steppe part of the province is dominated by '' Artemisia'' species and

Chenopodiaceae Amaranthaceae ( ) is a family of flowering plants commonly known as the amaranth family, in reference to its type (biology), type genus ''Amaranthus''. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 ...

genera. The Great Basin montane forests include ancient Great Basin bristlecone pine (''Pinus longaeva'') trees.

Californian province

The Californian province occupies Central and Southern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

from the seashore to the foothills of the

Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington (state), Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as m ...

, the

Sierra Nevada The Sierra Nevada ( ) is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primari ...

range, and northern parts of

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

. It possesses the most diverse flora within the floristic region. About half of the species are endemic. More than 50 genera (e.g. ''

Adenostoma ''Adenostoma'' is a genus of shrubs in the rose family (Rosaceae) containing only two species, chamise (''Adenostoma fasciculatum'') and redshanks ('' Adenostoma sparsifolium''). Both are native to the Californias. Description Characteristic ...

'', '' Bergerocactus'', ''

Carpenteria ''Carpenteria'' , the tree anemone or bush anemone, is a genus of flowering plants in the hydrangea family Hydrangeaceae. It is closely related to the similar genus '' Philadelphus'' and is monotypic, being represented by the single species '' ...

'', ''

Cneoridium ''Cneoridium'' is a Monotypic taxon, monotypic genus in the Rutaceae, citrus family which contains the single species ''Cneoridium dumosum'', commonly known as bushrue or coast spice bush. As a Perennial plant, perennial, evergreen shrub, ''Cneo ...

'', '' Dendromecon'', ''

Fremontodendron ''Fremontodendron'', with the common names fremontia and flannelbush or flannel bush, is a genus of three known species of shrubs native plant, native to the Southwestern United States and northwest Mexico. Taxonomy They are within the botanical ...

'', '' Jepsonia'', '' Lyonothamnus'', '' Neostapfia'', '' Odontostomum'', ''

Ornithostaphylos ''Ornithostaphylos'' is a monotypic plant genus which contains the single species ''Ornithostaphylos oppositifolia'', commonly known as the Baja California birdbush or Baja California manzanita. A large, evergreen shrub in the heather family, th ...

'', ''

Pickeringia ''Pickeringia'' is a monotypic genus of flowering plants in the legume family, Fabaceae. It was recently assigned to the unranked, monophyletic ''Cladrastis'' clade. It was named after the naturalist Charles Pickering. Its only species is ''Pic ...

'', '' Romneya'') are endemic or near-endemic as well. ''

Arctostaphylos ''Arctostaphylos'' (; from "bear" and "bunch of grapes") is a genus of plants comprising the manzanitas () and bearberries. There are about 60 species of ''Arctostaphylos'', ranging from ground-hugging arctic, coastal, and mountain shrub t ...

'', Brodiaeinae, ''

Calochortus ''Calochortus'' is a genus of flowering plants in the lily family. The group includes herbaceous, perennial and bulbous species, all native to North America (primarily the Western United States). The genus ''Calochortus'' includes mariposas ( ...

'', '' Caulanthus'', ''

Streptanthus ''Streptanthus'' is a genus of plants within the family Brassicaceae. There are 58 known species within the genus ''Streptanthus'', distributed through the western and south-central United States and northern Mexico. The common names for this gen ...

'', ''

Ceanothus ''Ceanothus'' is a genus of about 50–60 species of nitrogen-fixing shrubs and small trees in the buckthorn family (Rhamnaceae). Common names for members of this genus are buckbrush, California lilac, soap bush, or just ceanothus. ''"Ceanothus" ...

'', ''

'', '' Downingia'', '' Dudleya'', Eritrichieae, Eriogonoideae, Gileae, Hydrophyllaceae,

, '' Lotus'',

Madiinae Madieae is a Tribe (biology), tribe of flowering plants in the family Asteraceae. It is sometimes considered a subtribe of Heliantheae. Notable species include the tarweeds of the Western United States as well as the Silversword alliance, silver ...

, ''

Mimulus Mimulus , also known as monkeyflowers, is a plant genus in the family (biology), family Phrymaceae, which was traditionally placed in family Scrophulariaceae. The genus now contains only seven species, two native to eastern North America and th ...

'', Onagreae, Epilobieae, Orcuttieae, Eschscholzioideae, Platystemonoideae, ''

'' and ''

Cupressus ''Cupressus'' (common name cypress) is one of several genus, genera of evergreen conifers within the Family (biology), family Cupressaceae; for the others, see cypress. It is considered a Polyphyly, polyphyletic group. Based on genetic and morpho ...

'' have a principal center of diversity within the province. The flora of the Californian Province is partially shared with the spatially distant Chile-Patagonian region of the Antarctic kingdom and to a lesser extent Mediterranean region of the Holarctic kingdom. The vegetation of the Californian Province is varied. Wetter northern parts of the Californian province (

Northern California Northern California (commonly shortened to NorCal) is a geocultural region that comprises the northern portion of the U.S. state of California, spanning the northernmost 48 of the state's List of counties in California, 58 counties. Northern Ca ...

and

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

) as defined by

Peter Raven Peter Hamilton Raven (born June 13, 1936) is an American botanist and environmentalist, notable as the longtime director, now President Emeritus, of the Missouri Botanical Garden. Early life On June 13, 1936, Raven was born in Shanghai, China, ...

and D.I. Axelrod, as well as by

Conservation International Conservation International (CI) is an American nonprofit environmental organization headquartered in Crystal City, Virginia, in Arlington County, Virginia. CI's work focuses on science, policy and partnership with businesses, governments and co ...

, fall under the

Rocky Mountain region The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of Western Canada, to New Mexico in ...

in Takhtajan and Thorne's system and are not parts of the Madrean region.

Sonoran province

The Sonoran province comprises arid areas in the southwestern U.S. and northwestern Mexico from

and

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

and

Tamaulipas Tamaulipas, officially the Free and Sovereign State of Tamaulipas, is a state in Mexico; one of the 31 states which, along with Mexico City, comprise the 32 federal entities of Mexico. It is divided into 43 municipalities. It is located in nor ...

, including the Mojave (characterized by ''

Yucca brevifolia ''Yucca brevifolia'' (also known as the Joshua tree, yucca palm, tree yucca, and palm tree yucca) is a plant species belonging to the genus ''Yucca''. It is tree-like in habit, which is reflected in its common names. This monocotyledonous tree ...

'', Joshua Tree),

Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...

and Chihuahua Deserts. The vegetation is dominated by ''

Yucca ''Yucca'' ( , YUCK-uh) is both the scientific name and common name for a genus native to North America from Panama to southern Canada. It contains 50 accepted species. In addition to yucca, they are also known as Adam's needle or Spanish-bayon ...

'',

Cactaceae A cactus (: cacti, cactuses, or less commonly, cactus) is a member of the plant family Cactaceae (), a family of the order Caryophyllales comprising about 127 genera with some 1,750 known species. The word ''cactus'' derives, through Latin, ...

species (''

Opuntia ''Opuntia'', commonly called the prickly pear cactus, is a genus of flowering plants in the cactus family Cactaceae, many known for their flavorful fruit and showy flowers. Cacti are native to the Americas, and are well adapted to arid clima ...

'' spp. and other), as well as by ''

Larrea tridentata ''Larrea tridentata'', called creosote bush, greasewood, and chaparral is a medicinal herb. In Sonora, it is more commonly called ''hediondilla''; Spanish ''hediondo'' = "smelly". It is a flowering plant in the family Zygophyllaceae. The specific ...

'' (Creosote bush).

Mexican Highlands province

The Mexican Highlands province comprises areas in the

Mexican Plateau The Central Mexican Plateau, also known as the Mexican Altiplano (), is a large arid-to-semiarid plateau that occupies much of northern and central Mexico. Averaging above sea level, it extends from the United States border in the north to the T ...

region, including Madrean pine-oak woodlands.

Bibliography

*Thorne, Robert F
Phytogeography of North America North of Mexico
''

Flora of North America The ''Flora of North America North of Mexico'' (usually referred to as ''FNA'') is a multivolume work describing the native plants and naturalized plants of North America, including the United States, Canada, St. Pierre and Miquelon, and Greenla ...

'', Vol. 1, Ch. 6. {{Flora of the United States by political division Floristic regions * Natural history of Mexico Plant communities of the Western United States Plant communities of California Mexican Plateau * Natural history of the Colorado Desert Natural history of the Mojave Desert Holarctic

Floristic provinces

Great Basin province

Californian province

Sonoran province

Mexican Highlands province

See also

Bibliography