An evergreen shrub 2 to 4 ft high, young shoots, leaves (on both sides), outside of calyx-lobes, ovary, and flower-stalks all very scaly. Leaves oval, often inclined to oblong, rounded but with a tiny mucro at the apex, 1⁄2 to 3⁄4 in. long, 1⁄/6 to 1⁄3 in. wide, dark green above, yellowish grey between the scales beneath; stalk 1⁄12 to 1⁄8 in. long. Flowers opening in April and May in a terminal cluster of three to five, each on a very short stalk. Calyx 1⁄/6 in. long, deeply five-lobed, the lobes oblong, deep purple, fringed at the margin. Corolla 7⁄8 in. wide, of a rich plum-purple, the tube very short and clothed inside with white hairs, five-lobed, the lobes ovate-oblong, rounded at the end, spreading, sprinkled more or less with scales outside, mostly up the middle. Stamens normally ten, but sometimes as few as seven, purple, 1⁄2 in. long, tufted with white down near the base; anthers pale brown. Ovary scaly towards the top; style overtopping the stamens, purple, glabrous. (s. Lapponicum)
Native of N.W. Yunnan and S.W. Szechwan at 12,000 to 14,000 ft; discovered by Forrest in 1910 in the Lichiang range and introduced by him in the same year. Its flowers, although small, are of a wonderfully rich purple, this colour extending to the style and the filaments of the stamens. R. russatum, which often bears flowers of a similar colour, differs in having much larger leaves and a downy style. R. rupicola is perfectly hardy.
R. achroanthum Balf. f. & W. W. Sm. R. propinquum Balf. f. & Ward – This differs from R. rupicola in having five or six stamens only, and a more densely scaly ovary, but is probably not specifically distinct from it. It was introduced by Forrest in 1918 from the mountains north-east of Chungtien and is also in cultivation from seeds collected by Kingdon Ward in north-east upper Burma.
From the Supplement (Vol. V)
var. chryseum (Balf.f. & Ward) Philipson & Philipson – See R. chryseum, page 629; also Davidian, The Rhododendron Species, Vol. 1, pp. 177-9 (as R. chryseum), where the forms in cultivation are discussed. The variety is variable in the number of stamens.
var. muliense (Balf.f. & Forr.) Philipson & Philipson R. muliense Balf.f. & Forr. – Considered in recent years to be synonymous with R. chryseum, R. muliense is recognised as a distinct variety of R. rupicola by the Philipsons, similar in flower-colour to var. chryseum, but having the calyx-lobes margined with both hairs and scales (against hairs only in var. chryseum and var. rupicola), and with the leaves often narrowly oblong rather than elliptic. The traditional method of distinguishing the two species, as they once were, namely five stamens in R. chryseum and ten in R. muliense, does not work, since var. chryseum varies in the number of its stamens, though it is the case that they are fairly consistently ten in var. muliense (Rev. Lapp., pp. 62-3).
[R. achroanthum] – Included in R. rupicola.