''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 Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...

Rhododendron ''Rhododendron'' (; : ''rhododendra'') is a very large genus of about 1,024 species of woody plants in the Ericaceae, heath family (Ericaceae). They can be either evergreen or deciduous. Most species are native to eastern Asia and the Himalayan ...

'' species native to western

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 ...

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

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 ...

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 Cascade, or Cascading may refer to: Science and technology Science * Air shower (physics), a cascade (particle shower) of subatomic particles and ionized nuclei ** Particle shower, a cascade of secondary particles produced as the result of a high ...

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 primari ...

mountain ranges, but is not known east of them.

Description

''Rhododendron occidentale'' is a

shrub A shrub or 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 trees by their multiple ...

growing to 5 m tall. 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

, 3–9 cm long and 1–3 cm broad. The

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

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 soils 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'' 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 ''Rhododendron sect. Tsutsusi, Tsutsusi'' (evergreen) and ''Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate ...

s in Great Britain, such as the Exbury 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 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