An evergreen shrub 1 to 2 ft high; young shoots and leaf-stalks bristly. Leaves elliptic to obovate, tapered at the base, rounded at the apex, the mucro at the end often curiously reflexed, 11⁄2 to 23⁄4 in. long, 1⁄2 to 11⁄4 in. wide, dark glossy green and sparsely bristly above; glaucous and thickly set with shining yellowish scales beneath; stalk 1⁄4 in. long. Flowers terminal, mostly in pairs, sometimes solitary or in threes, opening in February or March. Calyx 1⁄3 in. long, with five deep, broadly ovate or obovate lobes, scaly only at the base, fringed with soft hairs; flower-stalk 1⁄4 in. long, scaly but not bristly. Corolla flat and open, 2 in. wide, pure white, with five broadly rounded, overlapping lobes; slightiy scaly outside, hairy in the throat. Stamens ten, their white stalks hairy except towards the top; anthers chocolate-brown. Ovary densely clad with whitish scales; style thick, curved, whitish, glabrous. Bot. Mag., t. 9665. (s. Boothii ss. Megeratum)
R. leucaspis was discovered by Kingdon Ward in the Tsangpo gorge, at the extreme eastern end of the Himalaya, in November 1924 (KW 6273). It was 'growing among rocks and beneath Bamboos, at the foot of a lofty cliff called the Musi La, or the Sulphur Mountain – there was a sulphur spring here, and I think it watered the Rhododendron. The slope immediately below the cliff was almost precipitous, and there were regular thickets of R. leucaspis dotted about here. It was not in flower, but I collected seeds, and it first flowered in this country in 1928' (Kingdon Ward, Gard. Chron., Vol. 94 (1933), p. 65). He reintroduced the species in 1926 from the Di Chu valley on the borders between Assam and Tibet (KW 7171), about 200 miles to the south-east of the original locality. This time too he never saw the species in flower. To complete the story of R. leucaspis, it was reintroduced by Ludlow, Sherriff, and Elliot in 1947 from the place where Kingdon Ward had originally found it (L.S. & E. 13549; Gard. Chron., Vol. 143 (1958), p. 102).
Few rhododendrons are held in greater affection than R. leucaspis, with its flowers so large in proportion to the size of the plant and the large chocolate anthers so oddly contrasting with their background of creamy white. It is perfectly hardy and has lived out-of-doors in many gardens for almost half a century, still retaining its dwarf habit. But the flowers, borne so early, are often destroyed by frost. It received an Award of Merit on February 12, 1929, when three plants were shown from Exbury by Lionel de Rothschild; they were less than 1 ft high and only four years old from seed, but bore flowers of the full size – about 2 in. across. At that time it was still known as Rhododendron KW 6273, but was named and described two months later. It was awarded a First Class Certificate in 1944.
R. megeratum Balf. f. & Forr. R. tapeinum Balf. f. & Forr. – This species is closely allied to R. leucaspis, differing in its yellow or cream-coloured flowers, in its densely bristly flower-stalks, and in the more glaucous undersides of the leaves. It was discovered by Forrest in 1914 on the Kari La, Mekong-Yangtse divide, growing on ledges of cliffs at 12,000-13,000 ft, and was introduced by him. Here it seems to be at the eastern end of its area, which extends westward into the eastern Himalaya, as far as the headwaters of the Subansiri. Forrest seems to have met with it only as a ground-dwelling plant, but in upper Burma and farther west it is often an epiphyte on fir or larch. It is mostly found between 10,000 and 12,000 ft. Bot. Mag., t. 9120.
R. megeratum is less easy to cultivate than R. leucaspis and less often met with as an outdoor plant. Also, some forms have flowers in rather uninteresting shades of yellow. The species received an Award of Merit when exhibited by Lord Swaythling on April 30, 1935 (plant raised from seeds collected by Kingdon Ward in 1926 in the Seinghku valley, N.W. upper Burma), and again on April 28, 1970, when shown from Bodnant by Lord Aberconway and the National Trust.