Quercus oblongifolia, commonly known as the Mexican blue oak, Arizona blue oak, Blue live oak or Sonoran blue oak, is an

evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional throughout the year. This contrasts with deciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many diffe ...

small tree or large shrub in the

white oak ''Quercus'' subgenus ''Quercus'' is one of the two subgenera into which the genus ''Quercus'' was divided in a 2017 classification (the other being subgenus ''Cerris''). It contains about 190 species divided among five sections. It may be calle ...

group.

Distribution

''Quercus oblongifolia'' grows in high

grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...

canyon A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency t ...

s and

mesa A mesa is an isolated, flat-topped elevation, ridge, or hill, bounded from all sides by steep escarpments and standing distinctly above a surrounding plain. Mesas consist of flat-lying soft sedimentary rocks, such as shales, capped by a ...

s in 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 ...

(

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 ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

and

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

) 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 ...

(

Baja California Sur Baja California Sur, officially the Free and Sovereign State of Baja California Sur, is a state in Mexico. It is the 31st and last state to be admitted, in 1974. It is also the second least populated Mexican state and the ninth-largest state by ...

, Chihuahua,

Coahuila Coahuila, formally Coahuila de Zaragoza, officially the Free and Sovereign State of Coahuila de Zaragoza, is one of the 31 states of Mexico. The largest city and State Capital is the city of Saltillo; the second largest is Torreón and the thi ...

Sinaloa Sinaloa (), officially the (), is one of the 31 states which, along with Mexico City, compose the Federal Entities of Mexico. It is divided into 18 municipalities, and its capital city is Culiacán Rosales. It is located in northwest Mexic ...

and

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 ...

states). Mexican blue oak is closely related to Engelmann oak "

Quercus engelmannii ''Quercus engelmannii'', the Engelmann oak or Pasadena oak, is a species of oak in the white oak section (''Quercus'' sect. ''Quercus''), native to Southern California and northwestern Baja California, Mexico. Description ''Quercus engelmannii'' ...

" in Southern California. The two species may be conspecific.

Description

The Mexican blue oak is a small

tree growing 5–8'' ''metres (16–27'' ''feet) tall with a rounded crown. At higher elevations it is typically a large shrub. The trunk is up to in diameter and the

bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...

is light gray and densely furrowed. The twigs are yellowish brown and hairless with reddish brown buds. The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are small, alternate and oblong, with entire margins, leathery, bluish-green above and mid green below. The flowers appear in spring at the same time as the old leaves are being shed and new leaf growth starts. The male flowers form yellowish-green catkins and the female flowers are solitary or paired and grow in the leaf axils. The light brown acorns are ovoid or oblong, about long and lodged in scaly, bowl-shaped cups about one third the length of the nut.

Habitat

The Mexican blue oak is common at elevations of 1,200 to 1,800'' ''m (4,000–6,000'' ''ft). It is often found on thin sandy soils in semi-arid regions and is the dominant species in lower open oak woodland where it grows in association with Arizona white oak (''

Quercus arizonica ''Quercus arizonica'', the Arizona white oak, is a North American tree species in the beech family. It is found in Arizona, New Mexico, western Texas, Sonora, Chihuahua, Coahuila, Sinaloa, and Durango. Description The Arizona white oak is o ...

'') and Emory oak (''

Quercus emoryi ''Quercus emoryi'', the Emory oak, is a species of oak common in Arizona (including inside Saguaro National Park), New Mexico and western Texas (including inside Big Bend National Park), United States, and northern Mexico (Sonora, Chihuahua (sta ...

''). It is an important constituent of pinyon–juniper communities. where it grows in association with species of

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...

and

juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' ( ) of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere as far south ...

, Arizona rosewood (''

Vauquelinia californica ''Vauquelinia californica'', commonly known as Arizona rosewood, is an evergreen species of shrub or tree, in the rose family, Rosaceae. The dark brown wood streaked with red, and is hard and very heavy, a beautiful 'rosewood.' It has dense whit ...

''), shrubby buckwheat ('' Eriogonum wrightii''), catclaw mimosa (''

Mimosa aculeaticarpa ''Mimosa aculeaticarpa'' is a species of woody shrub in the family Fabaceae. It is commonly known as the catclaw mimosa or the wait-a-minute bush, and is endemic to upland regions of Mexico and the Southwestern United States, particularly Ariz ...

''), bullgrass (''

Muhlenbergia emersleyi ''Muhlenbergia'' is a genus of plants in the grass family. The genus is named in honor of the German-American amateur botanist Gotthilf Heinrich Ernst Muhlenberg (1753-1815). Many of the species are known by the common name muhly. The greatest ...

''), plains lovegrass ('' Eragrostis intermedia''), fendlerbush (''

Fendlera rupicola ''Fendlera rupicola'', commonly known as the cliff fendlerbush or the false mockorange, is a shrub that grows in dry locations in the south central mountain regions of North America. Description The fendlerbush is a deciduous shrub that grows on ...

'') and wolftail (''

Lycurus phleoides ''Muhlenbergia'' is a genus of plants in the grass family. The genus is named in honor of the German-American amateur botanist Gotthilf Heinrich Ernst Muhlenberg (1753-1815). Many of the species are known by the common name muhly. The greatest ...

'').

Cultivation

Mexican blue oak "Quercus oblongifolia" popularity in landscaping has been increasing in California with many plantings at Apple Park and other Bay area plantings. The fast growth and beautiful blue foliage makes selections from trees in Arizona the best for cultivation.

References

{{Taxonbar, from=Q3414214 oblongifolia Trees of Northern America Plants described in 1853 Oaks of Mexico Flora of the Sierra Madre Occidental