An evergreen dwarf shrub with scaly minutely downy branchlets. Leaves elliptic to obovate-elliptic, rounded to obtuse at the apex, 1⁄2 to 3⁄4 in. long, about half as wide, bright green or bluish green above, glaucous and scaly beneath (sometimes with a few scales on the upper surface also); leaf-stalks very short, scaly. Flowers solitary, in twos or threes, from terminal buds; pedicels up to 1 in. long, elongating in fruit. Calyx five-lobed, scaly, up to 1⁄8 in. long. Corolla campanulate, five-lobed, 1⁄2 to 3⁄4 in. long, pink or rose-coloured, downy and slightly scaly outside. Stamens ten, included. Ovary densely scaly; style straight, included in the corolla, glabrous. (s. Uniflorum)
R. pumilum was discovered by J. D. Hooker in 1849 in the Sikkim Himalaya. It was, he wrote, the smallest of all the rhododendrons he saw. 'Its slender woody stem roots among moss, Andromeda fastigiata, &c., ascends obliquely, and bears a few spreading branches, 3 to 4 inches in length. . . . An extremely elegant species, and apparently very rare; for I have only gathered it twice, and each time in the wildest district of Sikkim, where its elegant flowers appear soon after the snow has melted, when its pretty pink bells are seen peeping above the surrounding short heath-like vegetation, reminding the botanist of those of Linnaea borealis.'
R. pumilum also occurs in E. Nepal, and to the east of Sikkim ranges as far as N.W. upper Burma. It was apparently not introduced, or at least not successfully, until Kingdon Ward found it on the Dohong La at the eastern end of the Himalaya in 1924, forming hassocks and mats on steep alpine turf. In 1926 he collected seeds from the Seinghku valley in Burma (KW 6961). This form, which he nicknamed “Pink Baby”, carried 'solitary or paired flowers of a delicate shell-pink, hoisted above the crowded leaves on long crimson stalks . . .'. More recently seeds have been sent by Ludlow and Sherriff and also by Stainton (from E. Nepal).
R. pumilum is very distinct from R. uniflorum and its immediate allies in its campanulate flowers and elliptic leaves. Indeed, it bears a certain resemblance to R. campylogynum. It is quite hardy and suitable for the rock garden. The Award of Merit was given on April 30, 1935, to a form raised from KW 6961, exhibited by Lord Swaythling, Townhill Park, Hants.
R. ludlowii Cowan – Allied to R. pumilum and of similar dwarf habit, but differing most markedly in its yellow flowers, spotted with reddish brown inside. The calyx is larger than in R. pumilum and leafy, and a further point of distinction is that the obovate leaves are faintly crenated at the edge. It was discovered by Ludlow and Sherriff in 1936 on the Lo La, a pass at 13,500 ft on the border between Tibet and Assam, near the source of the Siyom river, a tributary of the Brahmaputra. Two years later, they and George Taylor collected seeds a short way to the north, on Tsari Sama, Tibet, and from these the cultivated plants derive. Bot. Mag., n.s., t. 412.
R. ludlowii is not an easy plant to cultivate successfully. But Mr R. B. Cooke, who supplied the flowering piece figured in the Botanical Magazine, grew it successfully in Northumberland in a raised bed on the north side of a hedge, where it is screened from the sun for about six hours in the middle of the day. It is slow-growing, but bears flowers when the plant is still not much larger than its own corolla. Perhaps this rhododendron's chief claim to distinction is that it is a parent of the lovely 'Chikor' and 'Curlew', described in the section on hybrids.