Rhododendron occidentale

Western azalea


The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (flowering plants). Class - Magnoliopsida (dicotyledons). Subclass - Dilleniidae. Order - Ericales. Family - Ericaceae (heath). Genus - Rhododendron L. Species - Rhododendron occidentale (Torr. & A. Gray) A. Gray

Ecology: Western azalea usually grows in wetland or riparian habitats but not in areas where its roots would be submerged in water. It is tolerant of serpentine soils and is often a component of the unique plant communities found growing in this soil type in southwest Oregon. Western azalea is widely cultivated and is one of the most attractive and aromatic of all of the azaleas.


Habit: Hairs sparse to dense, glandular or not. Stem: <= 8 m, densely branched, hairy. Leaf: (2.5)3.5--8.2(10.8) cm, (0.8)1.2--2.9(3.6) cm wide, deciduous, margin ciliate. Inflorescence: short, 3--15-flowered, bracts red-brown, margins ciliate or glandular. Flower: corolla widely funnel-shaped, white to pink to salmon, upper petal yellow- to orange-blotched; stamens 5, +- equal. Fruit: longer than wide, dehiscing tip to base. Seed: ovate to fusiform, coat expanded around seed.


Pests and pathogens: Powdery mildew (Erysiphe vaccinii; formerly Microsphaera vaccinii) has been found only on wild R. occidentale growing on the southern Oregon coast. The disease is most common on deciduous azaleas but not as frequent on evergreen azaleas.


Flowering: Flowers grow in clusters (corymbs) of 5 to 20 and are typically very fragrant, at times detectable from over a 100 meters distance. Individual flowers are irregular with a 2 to 3 cm tube and spreading undulate lobes that have an approximate equal length to the tube. Petals are glandular pubescent on the outer surface and are white to pink in color with a yellow stripe. Some forms have a yellow blotch on one of the petals.

Species Distribution


USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant of the Week
Holmes, Russel. In: Wildflowers, Plant of the Week [Online]. U.S. Department of Agriculture, Forest Service.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA.

CalPhotos Photo Database. University of California Berkeley.
Photo credit: Br. Alfred Brousseau, Saint Mary's College.

PNW Plant Diseases
PNW Plant Disease Management Handbook. 2016 [Online]. Pacific Northwest Extension. Oregon State University.