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Species In Our Midst
Rhododendron luteum

by Susan Clark

Rhododendron luteum
Picture by S & J Perkins
Rhododendron luteum in Lincoln, MA

Rhododendron luteum

This deciduous azaleas is in Section Pentanthera. The geographical distribution of the species in Pentanthera reflects the antiquity of these azaleas; 12 are found in eastern North America, 1 in western North America, I in eastern Asia, and 1, R. luteum, in the Caucasus. Significantly, R. luteum is most closely related to R. occidentale from the West Coast and R. austrinum from the southeastern United States. How those landmasses move about! R. luteum is native in the Ukraine and the Caucasus, along the Turkish coast of the Black Sea and is found in some disjunct populations in what was Yugoslavia and in Poland.

R. luteum was first described by Linneus in 1753 as Azalea lutea.

It has had a great many different names (Azalea pontica, Anthodendron ponticum, Rhododendron ponticum, R. flavum, A. flava and so on) before the legal current name, first applied by Sweet in 1830, was settled on in this century. The specific name is a genuinely descriptive one, meaning 'yellow', referring to its lovely flowers.

R. luteum forms a small shrub, 4 to 6' in height, with an open, upright habit. It grows on open woody slopes and along streams, in swamps and near the sea at altitudes from sea level to 7000'. Its red-brown twigs are well covered with hairs, which often are gland-tipped. It has oblong (variably ovate, obovate or elliptic) leaves up to 4" in length; these are sparsely to densely covered with stiff, flat hairs. It flowers before or with the new growth of leaves. The inflorescence is a short raceme with up to 17 flowers. The flowers are 2". yellow with a darker yellow blotch on the upper petal, and nicely sweet. The pedicels (flower stalks) are densely hairy and glandular. The corolla tube is long, 3/4", and the stamens are over 2" long and exserted (protruding well beyond the corolla).

Greer rates its hardiness at -15° and gives it a good value rating of 3-4/3/4-5 (for flower, plant, and performance, respectively). Clement Brower, in his usually still useful book, Rhododendrons and Azaleas, says dismissively and erroneously that it is not hardy north of Philadelphia and R. calendulaceum is much preferable in this country (but not abroad). The Rhododendron Species Foundation just featured on its catalog cover their selected form of R. luteum, 'Golden Comet' with very large flowers and dark green foliage. This selection should help R. luteum's visibility among American growers.

R. luteum was a major parent of the famous Ghent hybrid azaleas. These are named after the city in Belgium where a baker named P. Mortier crossed R. luteum with several American azaleas. He kept his records secret, but it is widely assumed that he used R. calendulaceum, periclymenoides, and viscosum. L. Verschaffelt of Ghent acquired some of Mortier's best hybrids and continued the breeding program, followed by Casell, Vuylsteke and Van Houtte in Belgium and Waterer and Davies in England. The Ghent hybrids share the colors of their parents and provide a tremendous color range from the most brilliant colors to airy pastels. Usually the upper petal, site of R. luteum's blotch, is more vivid.

Over 100 Ghent hybrids were named and propagated, of which fewer than 25 are still in the trade today. They have been rather out of favor for years now, mostly because of the even more vivid and huge flowers of the Exbury hybrids. (Both have a predilection for powdery mildew, unfortunately.) Out of favor means out of production, so very few are now available in this country. My first azalea ever was the Ghent 'Daviesi', one of the English hybridizers, with its fragrant white flower and yellow blotch; I bought it from Weston Nurseries, who no longer offer it. This chapter just sold out a large batch of 'Narcissiflora' at the Convention sale; the buyers were lucky since it is a lovely, fragrant yellow and well worth growing!

Susan Clark, Concord, MA

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