An evergreen tree or large shrub up to 30 ft high; young shoots stout, clothed with silvery scurf. Leaves stiff and leathery, oblong to oblanceolate, tapered at both ends, 6 to 15 in. long, 3 to 6 in. wide, dark green and glabrous above, beautifully silvery or covered with dull tawny down beneath; stalk 1 to 2 in. long. Flowers sometimes twenty-five to thirty, opening during March and April in a rounded truss 5 to 7 in. wide. Calyx a mere rim; flower-stalk glandular, and it may be slightly downy, like the calyx. Corolla bell-shaped, 2 to 3 in. long and wide, ivory white, with conspicuous blotches at the base, eight-lobed. Stamens sixteen, downy at the base. Ovary downy and densely glandular; style glabrous or nearly so; stigma large, disk-like. Bot. Mag., t. 5054. (s. Grande)
Native of the Himalaya from Nepal eastward; described in 1847 from a specimen collected in Bhutan. In 1850 it was introduced from the Sikkim Himalaya by J. D. Hooker, who found it on Tonglo (west of Darjeeling) and Sinchul (S.E. of Darjeeling), both of which at that time lay within the domains of the Rajah of Sikkim. Hooker redescribed it under the name R. argenteum, which remained in use until well into this century and has not even now disappeared from garden nomenclature, though there is really no doubt that the Sikkim and Bhutan plants represent the same species. In this connection H. F. Tagg, the Edinburgh authority, wrote: 'In its typical condition [R. grande] is characterised by the oblong-oblanceolate leaves with their silvery undersurface. Forms occur in cultivation with a rougher and somewhat tawny indumentum. It was at one time thought that these might represent R. grande as opposed to R. argenteum with its more silvery under surface. There seems little doubt that R. argenteum is a synonym of R. grande' (The Species of Rhododendron, 2nd ed., p. 310). The synonymous name R. longifolium is founded on a narrow-leaved specimen collected by Booth in the Assam Himalaya.
One of the most magnificent of rhododendrons, this unfortunately can only be grown in the open air in the mildest counties. The finest examples are to be seen in Cornwall and western Scotland, where it has attained a height of over 30 ft.
R. sidereum Balf. f. – This is closely related to R. grande, but the leaves are as a rule narrower, only 11⁄4 to 23⁄4 in. wide, and up to 10 or 12 in. long, Corolla eight-lobed, bell-shaped, creamy white to yellow, with a crimson blotch at the base, nearly 2 in. wide. It was discovered in N.E. upper Burma in 1912 by Capt. Abbay, during the expedition that brought the frontier area around Hpimaw under British administration. Seven years later it was collected almost simultaneously in the Hpimaw area by Farrer and Cox, by Kingdon Ward, and by Forrest's native collectors, who, as Mr Cox records, came over the Hpimaw pass from China, much to Farrer's indignation (Farrer's Last Journey, p. 45). It was introduced the same year (Farrer 872 and Forrest 18054). According to Farrer it is a prevailing rhododendron in the upper forest zone around Hpimaw at 9,000 to 10,500 ft. Kingdon Ward sent seeds from the Seinghku valley, N.W. upper Burma, in 1926 (KW 6792), and from the Assam Himalaya in 1938 (KW 13649). Bot. Mag., n.s., t. 638.
R. sidereum is rather uncommon in cultivation and no more hardy than R. grande. It received an Award of Merit when shown from Brodick in the Isle of Arran on May 5, 1964 (clone 'Glen Rosa', with primrose-yellow flowers).