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Article from Bean's Trees and Shrubs Hardy in the British Isles
'Rhododendron chryseum' from the website Trees and Shrubs Online (treesandshrubsonline.
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A dwarf, evergreen, much-branched shrub 1 to 21⁄2 ft high; young shoots densely covered with a rather loose scurf of reddish scales, which become darker and fewer the second year, the bark of the branchlets becoming finally grey and peeling. Leaves stout, aromatic, oval, or inclined to obovate, mostly bluntish at both ends, 1⁄2 to 3⁄4 in. long, 3⁄16 to 5⁄16 in. wide, dark green, covered with shining scales above, paler and rather glaucous beneath with the scales less dense; stalk 1⁄12 in. long, scaly. Flowers deep sulphur yellow to pale yellow, four to six in a terminal cluster, opening in May. Corolla 3⁄4 to 1 in. wide, with a funnel-shaped base and five ovate lobes 3⁄8 in. long, slightly scaly outside, covered with white down in the tube. Stamens five to ten, 1⁄2 in. long, each with a tuft of white down at the base; ovary very scaly; style glabrous or slightly downy at the base. Calyx very scaly, five-lobed, the lobes oblong, 1⁄6 in. or less long. Bot. Mag., t. 9246. (s. Lapponicum)
R. chryseum is a species of alpine and subalpine scrub at 12,000 to 14,000 ft, from S.W. Szechwan through N.W. Yunnan to upper Burma. It was discovered by Kingdon Ward in 19.13 below one of the glaciers of Ka-kar-po, on the Mekong-Salween divide; introduced by Forrest five years later from the Beima-shan, a short way to the east of the type-locality, on the Mekong-Yangtse divide. The type of R. muliense, now included in R. chryseum, was collected in the Muli region of S.W. Szechwan.
In the original description the corolla of R. chryseum is described as golden, but in the plants from the first introduction, and from some later ones, they are too pale to deserve that term. It is very hardy and suitable for the rock garden but in many gardens it is not at all free-flowering and cannot be relied on as a foil for the purple- or lavender-flowered species of the Lapponicum series, and in any case blooms later than most of these.
In their revision of the Lapponicum group, M. N. and W. R. Philipson reduce R. chryseum to the status of a variety of the purple-flowered R. rupicola (q.v.), and give the same rank independently to R. muliense (here treated as synonymous with R. chryseum). Now that they have pointed it out, it becomes obvious that except in flower-colour there is really no difference between the two species. It is interesting that Kingdon Ward found R. chryseum growing in the upper Adung valley, Burma, in the company of purple-flowered plants that were in other respects indistinguishable from it (Gard. Chron., Vol. 93 (1933), pp. 170-1).
See R. rupicola, in this supplement.