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Species In Our Midst
Rhododendron rubiginosum

by Susan Clark

Rhododendron rubiginosum
Picture by S & J Perkins
Rhododendron rubiginosum in Conocrd, MA

Rhododendron rubiginosum

R. rubiginosum is a lepidote rhododendron in Section Rhododendron, Subsection Heliolepida. This subsection is related to Subsection Triflora, but is distinguished from it by its terminal flower clusters, more symmetric flowers and great density of scales. This is a rather homogeneous subsection and the distinction of its species is helped by their difficulty in cross-pollinating in the wild, due to very different bloom times.

R. rubiginosum grows over a wide area of China (in north, northwest, west and central Yunnan, in southwestern Sichuan and in southeastern Xizang) and in northeast Burma. It thrives in open woods and forest clearings, cane brakes, thickets, in open mountain pastureland and on granite boulders, all at altitudes of 7500' to 14,000'. It was first collected by the Abbé Delavay in 1886 in west Yunnan; it was described by Franchet in 1887. Delavay introduced it to Paris in 1889; it was reintroduced several times more by Kingdon-Ward, Rock and Yü.

R. rubiginosum ranges from a bushy shrub to a small tree, 2 to 30' high in cultivation. It somewhat resembles our native Carolina rhododendron, R. minus var. minus (R. carolinianum) in form, leaf shape and the purplish cast to its stems and leaves, but it is more erect and open. The leaves are evergreen, coriaceous (leathery), and usually somewhat shiny. They are elliptic, to about 3 1/2 " long, pointed, glabrous and elepidote above (hairless and scaleless) but wonderfully scaly below, with overlapping or contiguous scales of different size and color; these scales by their relative proportions make the undersurface range from pale green to rusty brown. The branchlets are also scaly.

The flowers of R. rubiginosum are usually at the ends of branches (terminal) in groups of 4 to 8, although some forms have axillary flowers as well. The corolla is broadly to narrowly funnel-shaped and up to 2" across with 5 petals in pink, lavender, purple, or white and all colors in between, with crimson or brownish spots. The flowers have 10 stamens, shorter than the length of the corolla; the stigma is longer than the corolla and projects outside the flower. The flower pedicel, calyx, the ovary and the seed capsule are all very scaly.

R. rubiginosum is rather rare on the East Coast and not considered especially hardy in the reference books. Its actual hardiness is a bit unclear, especially now that the more tender R. desquamatum has been rolled in with it. R. desquamatum blends in with R. rubiginosum at the western end of its area and contributes larger flowers and leaves along with its tenderness. This is another case where you have to check provenance of the plant. Greer rates it as hardy only to 0° and Leach rates it for H2. I got my plant from the Rhododendron Species Foundation in Seattle in 1991, where it was rated as hardy to 0° (I must have been feeling daring) and it has done just fine. We have not had a killer winter (below -8°) recently and the last few winters, after which it has flowered, have been comparatively mild. As a result I cannot say with certainty how hardy it and its buds are, but it least one form of it seems hardier than the book ratings.

Greer gives R. rubiginosum a very modest rating of 3/ 2-3 / 3-4 (5 is the top rating) for flower, plant & foliage, and performance, respectively. I would rate it higher on plant and foliage, since I very much appreciate its quiet elegance and odd coloration in the garden. From a distance, my plant looks grey/bronze (almost pinkish), a distinctive color against the dark green of most rhodies and the light green of the ferns behind it. After 10 years mine is not yet 4' high. The Coxes report that R. rubiginosum is free flowering and a favored plant at their garden in Scotland. Davidian also likes it, calling it "... a most desirably plant for every garden" and I agree. A heavy blooming clone 'Wakehurst' won an Award of Merit in the UK in 1960.

Susan Clark, Concord, MA

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