A large evergreen shrub or small tree up to 30 ft high. Leaves oblong-lanceolate, up to 11⁄2 ft long, 6 to 8 in. wide, broadest near the apex, tapered to a very short winged petiole (the wings really representing the decurrent base of the blade), blackish green, glossy and glabrous above, underside clad with a shining skin-like light grey or fawn indumentum. Flowers in a truss of twenty or sometimes more, opening in April or May; pedicels slightly over 1 in. long. Calyx minute. Corolla obliquely campanulate, eight-lobed, up to almost 2 in. long, pink or magenta-rose, with a crimson blotch in the throat. Stamens sixteen, glabrous. Ovary tomentose; style as long as the corolla or slighdy shorter, glabrous. (s. Grande)
Native of N.W. Yunnan, upper Burma, and the Assam Himalaya; discovered by Forrest in 1914on the Kari pass, Mekong-Yangtse divide, at 13,000 ft, and introduced by him. It is fairly near to R. sinogrande, but occurs at higher altitudes, and even out of flower is easily distinguished by the leaves being broadest near the apex and tapering at the base, where the blade reaches to the leaf-insertion, forming two wings along the petiole.
Dr Rock later collected seeds on the Mekong-Salween divide, also from 13,000 ft (Rock 59085 and 59462). Kingdon Ward's no. 13653 is from his 1938 expedition to the Assam Himalaya, and was collected on the Poshing La, where R. praestans ascends higher than any other big-leaved rhododendron and varies in the colour of its flowers from crimson to cerise and purple (Assam Adventure, p. 262).
R. praestans is one of the hardiest of the big-leaved rhododendrons and has proved to be wind resistant at Brodick in the Isle of Arran (R.C.Y.B. 1966, p. 26).
R. coryphaeum Balf. f. R. semnum Balf. f. – This is almost the same as R. praestans in its essential botanical characters, but the flowers are creamy white or pale creamy yellow. It was introduced by Forrest in 1918 from the Mekong-Salween divide in latitude 28° 12′. Rock's 59480 from the same area would seem to be intermediate between this species and R. praestans, judging from his field note, according to which the wild plants had flowers varying in colour from white to pink.
R. coryphaeum received an Award of Merit when shown by Edmund de Rothschild, Exbury, on April 18, 1963 (clone 'Exbury', with white flowers tinted with translucent yellow, blotched ruby-red in the throat).
R.semnoides Tagg & Forr. – This species resembles R. praestans in the short, winged petiole, but it is very distinct from it in the loose, woolly, brown indumentum of the leaf-undersides. It was discovered by Forrest on the Salween-Kiuchiang divide at 12,000 to 13,000 ft and was introduced by him from that locality in 1922. It seems to be rare in the wild and is not common in cultivation. Bot. Mag., n.s., t. 18.
From the Supplement (Vol. V)
R. coryphaeum, mentioned under this (page 745), is included in R. praestans. So too is R. semnum Balf.f. & Forr., not mentioned in the main work.
R. semnoides – Although hitherto placed in the Grande series, Dr Chamberlain considers that its proper position is in subsect. Falconera (Rev. 2, p. 253).