A dwarf evergreen shrub with scaly and sometimes shortly downy young stems. Leaves obovate or oblong-obovate, obtuse to rounded at the apex, 1⁄2 to 11⁄8 in. long, 1⁄4 to 1⁄2 in. or slightly more wide, dark green and slightly scaly above, the undersides glaucous and dotted with brown scales spaced up to one-and-a-half times their own diameter apart; petioles up to 1⁄8 in. or slightly more long. Flowers solitary or in pairs, terminal, on stalks up to 3⁄4 in. long at flowering-time, lengthening in fruit. Calyx small, scaly. Corolla five-lobed, widely funnel-shaped, 2 to 21⁄4 in. wide, purplish pink, scaly and hairy outside. Stamens ten, hairy at the base. Style slender, straight, usually glabrous, sometimes with a few scales or hairs at the base. (s. Uniflorum)
R. pemakoense was found by Kingdon Ward in fruit in 1924 during his winter journey through the Tsangpo gorge in the Tibetan province of Pemako, and was described by him in 1930 from the plants raised from the seeds he collected (KW 6301). Most of the seeds came from plants which he found on November 30 'on cliffs up the glens above the Tsangpo gorge, on Namcha Barwa and Sanglung'. But a small proportion was collected some days earlier at Pemakochung, and Kingdon Ward later came to doubt whether the specimens he collected in these two localities really represented the same species. There appears to be no record of any rogues having appeared from KW 6301, but it may be that the variation of R. pemakoense in cultivation, such as it is, is due to the fact that the seeds came from two localities.
R. pemakoense is one of the most delightful of dwarf rhododendrons, making a low, densely branched mound which, weather permitting, flowers so freely in March or April that almost every leaf is concealed by its large corollas. Unfortunately, the buds are liable to be killed by frost once they start to show colour. According to James Comber, a plant at Nymans, raised from the original seeds, bore 120 flowers in 1931, when six years old (Gard. Chron., Vol. 89 (1931), p. 375). In a later article he remarked that some plants there spread by underground runners, an unusual feature in Rhododendron.
An Award of Merit was given to R. pemakoense on April 24, 1928, when Sir John Ramsden showed a pan of seedlings a few inches high, bearing flowers described as white with a lilac flush outside, which is not the characteristic colour of the species and suggests that the pan may have come from a greenhouse. The plants were shown under the field number, as the species had not then been named.
R. uniflorum Hutch. & Ward – This species was described in 1930 from specimens collected by Kingdon Ward on the Doshong La, S.E. Tibet, at the end of June 1924 (KW 5876). He collected seeds in the following autumn. R. uniflorum is so like R. pemakoense that Cowan and Davidian were able to find only one difference that might be relied on, namely that in R. uniflorum the scales on the undersides of the leaves are more widely spaced, being three to six times their own diameter apart. If the two were united it would have to be under the name R. uniflorum, which has a few months' priority, but they decided to retain R. pemakoense as a separate species provisionally. It should be added that the type-localities of the two species are not much more than 10 miles apart as the crow flies.
From the Supplement (Vol. V)
In this species Dr Cullen includes R. patulum, mentioned on page 687 under R. imperator. It was placed there for the reason stated, and it should be added that Mr Davidian now submerges it in R. imperator altogether. This difference of opinion is, however, a matter only for botanists, since it is agreed that plants grown as R. patulum are R. pemakoense.
For R. uniflorum, mentioned under R. pemakoense, see this supplement, in alphabetical order.