An evergreen shrub found by collectors varying from 6 to 30 ft high; young shoots scaly. Leaves oval-lanceolate, wedge-shaped to rounded at the base, usually sharply pointed, 11⁄2 to 3 in. long, 3⁄8 to 11⁄4 in. wide; dark green and with a few scales above, very glaucous or bluish white and scaly beneath, the scales well apart from each other; stalk 1⁄8 to 1⁄3 in. long. The margin of the leaf is fringed with hairs when young, but most of them fall away. Flowers produced in March or April from the end of the shoot and the axils of the terminal leaves in umbels of three to five, slightly fragrant; flower-stalk 2⁄5 in. long, scaly. Calyx small, shallowly bowl-shaped, with a few hairs on the margin. Corolla rosy white, 1 to 15⁄8 in long, funnel-shaped at the base, expanding at the mouth into five oval rounded lobes, scaly all over the outside. Stamens ten, slightly downy towards the base. Ovary scaly; style glabrous. Bot. Mag., t. 8878. (s. Triflorum ss. Yunnanense)
Native of N.W. Yunnan and bordering parts of upper Burma; discovered by Forrest in 1912 on the Shweli-Salween divide and introduced by him in that year. The most striking character of this rhododendron is the intensely glaucous white undersurface of the leaves, due to a coating of wax. Although the flowers are typically white or pink, plants with flowers coloured as in R. ponticum were found by Farrer and Cox in Burma (Farrer 980), and a yellow-flowered form was introduced by Kingdon Ward in 1953 from the Triangle between the two branches of the upper Irrawaddy. Having a wide altitudinal range, from 6,000 to 13,000 ft, it is variable in hardiness, but Forrest’s original introduction was perfectly hardy. R. zaleucum is unusual among its allies in that it sometimes grows as a small tree in rain-forest; as a general rule the species of the Yunnanense subseries prefer more open habitats.
R. zaleucum received an Award of Merit when shown by Col. S. R. Clarke, Borde Hill, Sussex, on May 24, 1932 (flowers mauve-pink, slightly spotted).