''Rhododendron occidentale'', the western azalea or California azalea, is one of two

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...

Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the heath family (Ericaceae). They can be either evergreen or deciduous. Most species are nat ...

'' species native to western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the C ...

(the other is '' Rhododendron albiflorum''). The western azalea is known to occur as far north as Lincoln and

Douglas Douglas may refer to: People * Douglas (given name) * Douglas (surname) Animals * Douglas (parrot), macaw that starred as the parrot ''Rosalinda'' in Pippi Longstocking * Douglas the camel, a camel in the Confederate Army in the American Civi ...

Counties in

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

and as far south as the mountains of San Diego county. Typically found in the coastal ranges of western North America, it also grows in the Cascade and

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 primarily ...

mountain ranges, but is not known east of them.

Description

''Rhododendron occidentale'' is a

shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from tree ...

growing to 5 m tall. The

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

are

, 3–9 cm long and 1–3 cm broad. The

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...

s are 3.5–5 cm diameter, with five lobes on the corolla; color varies from white to pink, often with a yellow blotch. There is considerable diversity in the form and appearance of this species, with genetic diversity seeming to reach its highest level along the coast in the vicinity of the border between Oregon and California. It is tolerant of

serpentine soil Serpentine soil is an uncommon soil type produced by weathered ultramafic rock such as peridotite and its metamorphic derivatives such as serpentinite. More precisely, serpentine soil contains minerals of the serpentine subgroup, especially ...

s to the point that serpentine soils (along with surface water) can be used as a sign of its presence in southern Oregon. For this reason, it is a part of the unique plant community found in the serpentine barrens of the

Siskiyou Mountains The Siskiyou Mountains are a Coast Ranges, coastal subrange of the Klamath Mountains, and located in northwestern California and southwestern Oregon in the United States. They extend in an arc for approximately from east of Crescent City, Calif ...

, along with ''

Darlingtonia californica ''Darlingtonia californica'' , also called the California pitcher plant, cobra lily, or cobra plant, is a species of carnivorous plant. It is the sole member of the genus ''Darlingtonia'' in the family Sarraceniaceae. This pitcher plant is nativ ...

'' and '' Cypripedium californicum''. It is usually found in wetlands although, like other rhododendrons, it does not grow with its roots submerged in water. It prefers both more moisture and more sunlight than '' Rhododendron macrophyllum'', an evergreen rhododendron with a similar range.

History and cultivation

''Rhododendron occidentale'' was described by explorers in western North America in the nineteenth century. At one time, the various geographic races were each classified as separate species. Seed was sent to Veitch Nursery in England in 1850 by William Lobb. The western azalea was an early contributor in the development of deciduous hybrid

azalea Azaleas are flowering shrubs in the genus ''Rhododendron'', particularly the former sections '' Tsutsusi'' (evergreen) and '' Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate Northern Hemisphere, and Octo ...

s in Great Britain, such as the

Exbury Exbury is a village in Hampshire, England. It is in the civil parish of Exbury and Lepe. It lies just in the New Forest, near the Beaulieu River and about a mile from the Solent coast. It is best known as the location of Exbury House, built ...

azaleas. During the twentieth century it has been the subject of ongoing plant exploration as at least three generations of rhododendron enthusiasts have sought out unusual forms for use in the garden and to record for science. Many of those forms are now conserved in the Smith-Mossman Western Azalea Garden at

Lake Wilderness Arboretum Lake Wilderness Arboretum (40 acres), known for a time as the South King County Arboretum, is an arboretum in Maple Valley, Washington. The arboretum is open daily without charge. It is located off the Lake Wilderness Trail. In addition to a focus ...

in Maple Valley, Washington state, USA.

References

* Galle, Fred C. ''Azaleas''. 1987, second printing 1991. Timber Press. . * Davidian, H. H. ''The Rhododendron Species, Volume IV - Azaleas''. 1995. Timber Press. . * Cox, Peter A. & Kenneth N.E. ''The Encyclopedia of Rhododendron Species''. 1997. Glendoick Publishing. . * Towe, L. Clarence ''American Azaleas''. 2004. Timber Press. .

External links

* *
Jepson Flora Project: ''Rhododendron occidentale''

Western Azalea Garden: ''Rhododendron occidentale'' photos
- '' Maple Valley, Washington'' {{Taxonbar, from=Q1129673 occidentale Flora of California Flora of Oregon Flora of the Sierra Nevada (United States) Garden plants of North America Flora of Northern America Plants described in 1857