QBARS - v28n2 The Western Azaleas, Rhododendron occidentale

The Western Azalea, Rhododendron occidentale
Frank Mossman, M. D., Vancouver, Washington

Britt Smith of Kent, Washington and I have been researching Rhododendron occidentale for eight years. About 275 clones have been catalogued for study in the field and at our homes. We were inspired in part by Leonard Frisbie of Tacoma, Washington, who spent many years in field and library study of this species. The only clone to receive a registered name by Britt or me has been called R. occidentale variety 'Leonard Frisbie' by Britt Smith who found the plant, a truly splendid tribute to a friend. This clone is available in the trade throughout the Northwest and several other areas of the world to which it has been freely distributed.

J. B. Stevenson ¹ gave a brief description of R. occidentale. The following data will hopefully give a further understanding of leaf and flower bud variations seen by us on this seemingly unpredictable shrub in its native situation. The description is not complete and is intended as a supplement to Stevenson. Just as the flowers vary considerably, so do the leaves. The variety of the late summer and autumn color is another reward.

Leaves:

Deciduous, chartaceous to thicker. Lamina outline: elliptic, ovate, obovate or oblanceolate; several leaf forms may be found on one plant.

Base: cuneate.

Apex: acute or obtuse, usually mucronate.

Form: flat, recurved, dorsally curved on long axis of leaf, crispate or wavy margins, or twisting of the leaf on its long axis.

Margins: entire, or occasionally sinuate.

Surface sheen: dorsum shiny or sometimes not, ventrum not shiny. Color: dorsum deep jade green to pale yellowish-green, or copper-like to plum color, the latter total or partial and rarely in dot like concentrations. Mid rib paler green, or often on its ventrum shades of red. Lamina ventrum, pale green.

Mucro: usually present, a fraction of a millimeter in length and width. The mucro may be a definite projection from the lamina or a widening of the mid rib within the lamina. The mucro is sometimes absent. The color is pale green or less often shades of red. The tip is blunt or even slightly broader than base.

Size: 5 to 40 millimeters wide by 15 to 96 millimeters long.

Elsewhere ² R. occidentale flowers have been described in detail with pictures of several forms in black and white and color pictures of R. occidentale 'Leonard Frisbie' and SM Stagecoach Frills, with discussion of the considerable variation in flower size, form, and color. A summary of this information follows:

Inflorescence: 6 to 51 flowers per truss (one rachis) expanding with or occasionally before the leaves.

Corolla: tubular campanulate or tubular salver form; 9 to 102 millimeters across the flower face. The deep pink or red flowers or extra-petal flowers are smaller. The upper petal usually solid or speckled yellow to orange, occasionally same colors present on upper wing petals, rarely on all petals, rarely upper petal yellow tints absent. Inside of petals white, cream, pink, red, or deep red; or combinations of these colors in stripes or dots, variously combined on the standard with yellow to orange; rarely complete or incomplete red margination or very rarely dark red splotches over all with white interstices;3 outside of petals pink and white, deep pink to red or pink with green and white rarely pure white, always deeper pink on the outside than on the inside. Five petals but sometimes supernumerary petals with no petalloidy of calyx or filaments; substance chartaceous, sometimes subleathery; petal surface flat or with longitudinal folds (crepe-like) and twisted; petal margins entire, occasionally frilled, or notched, or rarely serrated; tube lumen, only a potential space especially at area of emergence of organs at flower face. Flower face: symmetrical star shape or asymmetrical rarely with lower two petals in near horizontal position or almost straight down; or square-faced because of broad petals.

Stamens: Usually 5: seldom 6 to 10; about as long as corolla: rarely very short; partial or complete petalloidy to give up to 15 petals per floret.

Pistil: Somewhat longer than stamens; the tube white, pink, or red, stigma small to prominent knob-like form and yellow, green, red, deep red, or gray-colored. The stigma emerges first from the opening corolla tip well away from the proximally folded filaments with anthers held in the throat of the unopened bud. Rarely more than one pistil per floret.

Fragrance: Very prominent, sweet, abundant on a warm afternoon. New leaves have a skunk-like odor, not penetrating, persisting for a few days.

Capsule: 13 millimeters to 32 millimeters long; green, yellow-green, red or deep red.

Blooming time: April, May, June, and July. Main bloom in May-June, an occasional flower in any month along the coastal areas. Often develops next flower buds at almost same time as bloom. Some plants bloom fully in August or September, annually.

Flower Buds:

Number: Usually one per terminal branch but up to nine have been observed.

Outline: Ovate, at times lanceolate or sub-orbicular.

Color of scales: Green, or green with red mid rib-like elevation, or entirely red, or pale to deep purple-red. Often with thin white upper margins.

Scale form: The outer basal two or three scales are more narrow and elongate than the inner scales and terminate in an aristate tip or a narrow leaf-like form a few millimeters in length to longer than the flower bud. The remaining scales are broader and imbricated to an acute tip.

Size of buds: 5 to 8 millimeters wide x 10 to 19 millimeters long.

The average R. occidentale flower bud is somewhat larger than that of the other native American azalea species. The Knaphill hybrid azalea flower buds are generally similar in size and shape to R. occidentale , a major ancestor of Knaphills.

Distribution and Cold Tolerance
R. occidentale grows at high altitudes where it is resistant to extreme cold and seems to do well in near desert situations where it must survive heat and periods of drought. It thrives along the coast of northern California where the humidity is high and the temperatures are mild; selected clones from this latter area are also cold resistant. We had questioned the cold tolerance of coastal varieties until our last Northwest winter with temperatures down to -12° F. and gale winds, a test survived without apparent damage to wood or buds. Distribution of R. occidentale is generally given as California and southwestern Oregon. Island populations are seen elsewhere. Lawrence Pierce of Seattle, Washington reports that R. occidentale was native to his place on Puget Sound. We believe it may be on the Olympic Peninsula and Mount Rainier. Comments are invited.

Hybridizing with R. occidentale
Hybridizing with R. occidentale presents some exciting possibilities. As the female parent, R. occidentale will cross with a great many azalea species and hybrids, and evergreen rhododendrons too, including some lepidotes! As the pollen parent, R. occidentale crosses only occasionally. Anthony Waterer Sr., of Knaphill Nursery, England, was the first known hybridizer of R. occidentale in the 1860's and reportedly had little success for almost ten years. It is probable that he had pollen only, at first, and later had flower-producing plants to use for seed parents. His effort with the Ghent Azaleas plus R. occidentale was the beginning of the Knaphill Azaleas and later the Exburys.

Some of my crosses follow:

R. occidentale x R. lindleyi produces plants with semi-evergreen rather bullate leaves.
R. occidentale x R. 'Loderi' gives large-leafed semi-evergreen plants.
R. occidentale x R. hemsleyanum plants are similar to the above.
R. occidentale x R. schlippenbachii .
R. reticulatum , or R. amagianum have not been fruitful for me.
R. occidentale x R. calendulaceum , R. prunifolium , R. austrinum , R. canescens , R. bakeri , or R. viscosum produce viable seed.
R. prunifolium , R. bakeri , or R. viscosum x R. occidentale will take.
( R. occidentale x R. bakeri ) x many of the Knaphill azaleas succeed.
( R. occidentale x R. prunifolium ) x several eastern American azalea species succeed.
A R. occidentale clone x self usually produces no or only a few weak seedlings.
Hand-pollinated intra-specific R. occidentale crosses take readily and produce vigorous seedlings, generally. Because of the foregoing, it is apparent that open-pollinated domestic seed cannot be expected to reproduce pure R. occidentale. Future articles will describe flowers of R. occidentale hybrids.

References:

1. The Species of Rhododendron by J. B. Stevenson, 1930.
2. Quarterly Bulletin of American Rhododendron Society, Volume 26, #4, 1972
3. Quarterly Bulletin of American Rhododendron Society. Volume 25, #4, 1971