An evergreen shrub usually not more than 10 ft high in the wild; bark peeling; young shoots glabrous. Leaves oval, 3 to 51⁄2 in. long, 11⁄4 to 21⁄2 in. wide; abruptly tapering at the apex, tapering, rounded, or slightly heart-shaped at the base, glabrous above, densely covered beneath with a red-brown felt; stalk 1⁄2 to 1 in. long, often reddish. Flowers rosy purple of numerous shades, or almost white, 2 in. across, produced during April in rather loose clusters about 4 in. wide. Calyx downy, small and scarcely lobed. Corolla broadly bell-shaped, with five notched lobes, the upper ones dark purple-spotted. Stamens ten, glabrous or sometimes downy towards the base; flower-stalk about 1 in. long. Bot. Mag., t. 3759. (s. Campanulatum)
Native of the Himalaya from Kashmir to some way east of Bhutan, from 10,000 to 14,000 ft. According to Loudon, Loddiges' nursery received seeds from Wallich in 1825, but there may have been earlier introductions to private gardens. In 1844 it was referred to as 'one of the best hardy evergreens we have' (Gard. Chron. (1844), p. 379). It is very variable in the colour of the flowers, which are sometimes quite pale, sometimes of a bright bluish purple, sometimes lilac or even white; in the amount of felt at the back of the leaf; and in the colour of the leaf-scales that accompany the young bursting shoots, which are sometimes rich crimson, sometimes green. At its best it is a beautiful rhododendron, though not held in much regard at the present time. In Scotland it has attained a remarkable size, e.g., 30 ft in height and 41⁄2 ft in girth at breast height at Benmore, Argyll (R.C.Y.B. 1964, p. 13; op. cit., 1968, fig. 17).
cv. 'Knap Hill'. – Flowers large, of a beautiful shade of blue-mauve. Raised at the Knap Hill Nursery. Award of Merit when shown from Exbury, May 5, 1925.
Two other forms that have received the same award are: 'Roland Cooper' and 'Waxen Bell', both exhibited by the Royal Botanic Garden, Edinburgh (see R.C.Y.B. 1965, p. 166, and op. cit., 1966, p. 163).
var. aeruginosum (Hook, f.) Hook. f. R. aeruginosum Hook. f. – Young leaves glabrous above, described by J. D. Hooker as 'of a verdigris hue'. He found it in Sikkim growing with R. fulgens at 13,000 to 15,000 ft, and at first considered it to be a distinct species. It is cultivated only for the beauty of its young foliage.
R. wallichii Hook. f. R. campanulatum var. wallichii (Hook. f.) Hook. f. – In Species of Rhododendron this is distinguished from R. campanulatum by the undersides of the leaves being sparsely dotted with tufts of hair, in contrast to the continuous felt of the other species. However, Cowan and Davidian have pointed out that the indumentum in R. campanulatum is sometimes quite as sparse as in R. wallichii. The difference between them lies in the nature of the hairs themselves: in R. campanulatum they are slender-stemmed, with numerous long thread-like branches, in R. wallichii they are stout-stemmed, with short, broad branches (R.Y.B. 1949, p. 176). Since microscopic hair-structure is an important taxonomic character in Rhododendron, R. wallichii is recognised as a distinct species, though it does not otherwise differ from R. campanulatum. It is figured in Bot. Mag., t. 4928, and its known range is from Nepal to the Assam Himalaya.
From the Supplement (Vol. V)
subsp. aeruginosum (Hook.f.) Chamberlain R. campanulatum var. aeruginosum (Hook.f.) Cowan and Davidian; R. aeruginosum Hook.f. – This has a more easterly distribution than the typical subspecies, but there is some overlap (Rev. 2. p. 373).
cv. 'Graham Thomas'. – A seedling of great promise, raised at the Knap Hill Nursery, Surrey, with good foliage and lavender blue flowers. Registered 1985 and propagated.