western azalea

Rhododendron occidentale

Summary 4

Rhododendron occidentale, the Western Azalea, is one of two deciduous Rhododendron species native to western North America (the other is Rhododendron albiflorum). The Western Azalea is known to occur as far north as Lincoln and Douglas Counties in Oregon 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 mountain ranges, but is not known east...

Habitat 5

 

Moist wooded slopes and canyon bottoms, along rivers and streams, shrub thickets, Darlingtonia bogs, serpentine ridges, ocean bluffs

 

History and cultivation 4

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 azaleas 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.

Diagnostic description 6

 

Shrub or small tree to 8(-10)m tall, usually non-rhizomatous; young twigs red-brown, rarely yellow-brown, grey or glaucous, sparsely to densely covered with unicellular hairs and multicellular gland-tipped hairs or glabrous, occasionally sparsely to densely covered with only unicellular hairs. Vegetative bud scales glabrous or sparsely covered with unicellular hairs and multicellular eglandular hairs abaxialiy; margin unicellular-ciliate or glandular. Leaf blade membranaceous, ovate or obovate to elliptic, (2.5-)3.5-8.2(-10.8) x (0.8-)1.2-2.9(-3.6)cm; base acute to obhque; apex acute to obtuse, often mucronate; adaxial surface sparsely covered with unicellular hairs and multicellular eglandular or gland-tipped hairs, with only multicellular eglandular hairs, the multicellular gland-tipped hairs, or both, or glabrous, the midvein densely covered with unicellular hairs, rarely also with multicellular gland-tipped hairs or eglandular hairs; abaxial surface glabrous, sparsely covered with unicellular hairs, multicellular gland-tipped hairs or both, rarely with multicellular eglandular and glandular hairs, midvein sparsely covered with multicellular eglandular hairs or with unicellular hairs and multicellular gland-tipped hairs, rarely with unicellular hairs and multicellular eglandular hairs or with only multicellular gland-tipped hairs; margin entire, ciMate with multicellular eglandular hairs or with multicellular eglandular and gland-tipped hairs; petiole (0.1-)0.2-0.5(-1.0)cm long, sparsely to densely covered with unicellular hairs and multicellular eglandular or gland-tipped hairs, rarely with all three types of hairs. Flower bud scales chestnut brown; abaxial surface sparsely to densely covered with unicellular hairs, rarely also with sparse multicellular eglandular or gland-tipped hairs; margin unicellular-ciliate or glandular. Flowers appearing with the leaves or after they have expanded; inflorescence a shortened raceme of 3 to 15 flowers. Pedicels (0.9-)l.l-2.0(-2.6)cm long, covered with multicellular gland-tipped hairs, occasionally with multicellular eglandular hairs. Sepals 0. l-0.4(-0.9)cm long, often varying in length on the same flower; margins glandular-fimbriate, rarely setose; abaxial surface sparsely to densely covered with unicellular hairs and multicellular gland-tipped hairs or with only multicellular gland-tipped hairs, occasionally glabrous or with unicellular hairs and multicellular eglandular hairs, rarely with only multicellular eglandular hairs. Corolla white, with a yellow blotch on the upper corolla lobe, white and pink or salmon, or pink with an orange blotch on the upper corolla lobe, rarely white with yellow lines at the throat, or with the tube white to red, fragrance sweet or mephitic, the tube longer than the Emb and gradually expanding into it; upper corolla lobe (1.3-) 1.4-2.3(-2.8) x 1.2-2.1(-2.6)cm; lateral lobes (1.5-)1.7-2.4(-2.9) x (0.7-)0.9-1.4(-1.7)cm; corolla tube (1.5-)1.8-2.6(-2.9)cm long, (0.2-)0.3-0.5(-0.6)cm wide at base; outer surface of corolla sparsely to densely covered with unicellular hairs arid multicellular gland-tipped hairs that continue up the corolla lobes, rarely also with multicellular eglandular hairs; inner surface of corolla sparsely to densely covered with unicellular hairs, occasionally glabrous. Stamens (4.0-)4.6-6.3(-7.5)cm long, with dense terete or flattened unicellular hairs on proximal (1.8-)2.1-3.3(-3.6)cm of filament, exserted (2.4-)3.0-4.2(-4.7)cm beyond throat of corolla. Style (4.1-)4.6-6.6(-8.2)cm long, exserted (2.6-)3.3-4.8(-5.3)cm beyond throat of corolla, with dense unicellular hairs on the proximal (0.2-)0.3-L0(-L3)cm; stigma 0.1-0.3cm wide. Ovary 0.2-0.4(-0.5)cm long, (0. l-)0.2-0.3(-0.4)cm wide at the base, densely covered with unicellular hairs and multicellular eglandular and gland-tipped hairs, or lacking multicellular eglandular hairs, with a dense crown of unicellular hairs along the nectary, rarely with only multicellular eglandular or gland-tipped hairs or both. Capsules (1.2-)1.3-1.8(-2.2) x (0.4-)0.5-1.0(-1.4)cm, sparsely covered with unicellular hairs and with multicellular eglandular or gland-tipped hairs. Seeds pale to dark chestnut brown, ovate or elliptic to fusiform, (1.0-)1.5-2.3(-3.0) x(0.5-)0.7-l.l(-1.5)mm,body(0.6-)0.8-1.4(-1.6)x(0.2-)0.3-0.5(-0.7)mm; testa expanded and dorsiventrally flattened, surrounding the body, the cells essentially isodiametric, with transverse end-walls

 

National nature serve conservation status 7

United States
Rounded National Status Rank: N5 - Secure

Sources and Credits

  1. (c) Eric in SF, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/39312862@N00/150158456
  2. (c) phoca2004, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/phoca2004/9088070619/
  3. (c) Eric Hunt, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/ericinsf/150147562/
  4. Adapted by dlimandri from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Rhododendron_occidentale
  5. (c) Royal Botanic Garden Edinburgh, some rights reserved (CC BY-NC), http://eol.org/data_objects/17267318
  6. (c) Royal Botanic Garden Edinburgh, some rights reserved (CC BY-NC), http://eol.org/data_objects/17267315
  7. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/14786069

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