An evergreen shrub occasionally up to 12 ft in the wild, but dwarf at high altitudes; young branchlets scaly and bristly. Leaves elliptic or slightly obovate, 2 to 4 in. long, 3⁄4 to 11⁄2 in. wide, rounded or obtuse at the apex, slightly narrowed at the base, densely scaly beneath, fringed with hairs when young; petioles up to 3⁄4 in. long. Inflorescence a terminal truss of usually three or four flowers, opening in April or May; pedicels about 3⁄8 in. long, scaly. Calyx very short, oblique, fringed with long hairs. Corolla funnel-shaped, five-lobed, about 21⁄4 in. long, 3 in. wide, scaly on the outside, very fragrant, variable in colour, but typically white with a rose-purple flush along the midrib of the lobes on the outside, yellow on the upper side of the throat and with some crimson spotting on the upper lobe; sometimes pure white with a purple flush, or creamy white with a yellow tinge in the throat but with no hint of pink or purple. Stamens ten, downy in the lower half. Ovary scaly, style scaly except near the apex. Capsule six-celled. (s. Maddenii ss. Ciliicalyx)
Native of Assam, in the Naga Hills and Manipur; discovered by Sir George Watt early in 1882 in several localities at 6,000 to 11,000 ft; he named it after the wife of the Political Agent in Manipur and sent seeds and specimens to Kew, with detailed field notes, but the species was not described until 1919.
One of the summits on which Sir George Watt found this species was Mt Japvo in the Naga Hills, near the border with Manipur, near Kohima, and it was introduced from there by Kingdon Ward in 1927 (the seedlings from Watt's sending all eventually died off). Seven years later the species received an Award of Merit when exhibited by Lt-Col. L. C. R. Messel of Nymans, Sussex. In the plant shown, the flowers were creamy white with a yellow blotch inside on the upper part of the tube. In 1941 the same award was given to a plant under the distinguishing name 'Rubeotinctum', in which each lobe is striped with pink on the outside and there is a pink flush in the yellow patch in the throat. This was shown by Lt-Col. Bolitho of Trengwainton, Cornwall, and is actually the more typical form. But both plants were raised from the same batch of seed (KW 7732).
R. johnstoneanum is perhaps the hardiest member of the Ciliicalyx subseries after R. ciliatum and has lived out-of-doors in several gardens in southern England ever since it was first introduced almost half-a-century ago, though the finest plants are to be found in the milder parts.
R. johnstoneanum has produced plants with more or less double flowers. A clone with fully double flowers named 'Double Diamond' received an Award of Merit on April 17, 1956 (R.C.Y.B. 1957, fig. 29).
R. lyi Lévi. – Related to R. Johnstoneanum, differing in its narrower leaves and less bristly shoots, but perhaps not specifically distinct. If the two species were to be united, as they have been by Dr Sleumer, then the combined species would have to take the name R. lyi, which has priority.
R. lyi was discovered in Kweichow, Central China, by a native collector Jean Ly, working for the French missionaries, and was introduced to Europe by seeds which they sent to M. Vilmorin. It is rather tender, and not common in cultivation. Bot. Mag., t. 9051.
From the Supplement (Vol. V)
This species is probably not confined to Manipur. In 1956 Kingdon Ward collected a rhododendron in western central Burma on the Mindat ridge (KW 22200) which is very like R. johnstoneanum and may be a minor variant of it lacking the ciliation of the leaves (Rev. 1, 47).
R. johnstoneanum was sunk by Dr Sleumer in R. lyi (mentioned under it on page 694), but the two are quite distinct. R lyi is closely allied to R. ciliicalyx (q.v. in this supplement).
R. dendricola Hutch. R. taronense Hutch; R. notatum Hutch.; R. atentsiense Hand.-Mazz. – This is placed by Dr Cullen in the R. johnstoneanum aggregate, which has many characters in common with the Ciliicalyx aggregate, differing in having the base of the style sunk in a depression at the top of the ovary (in the Ciliicalyx aggregate the top of the ovary is more or less tapered into the style).
R. dendricola is usually an epiphyte, growing in jungly, warm temperate forest. Its essential characters are: leaves larger than in R. johnstoneanum, 3 to 5 in. long. 11⁄8 to 2 in. wide, elliptic to narrowly obovate, acute or acuminate, mostly tapered at the base, from distantly to fairly densely scaly beneath. Inflorescence of three to five flowers. Calyx shortly lobed or reduced to a rim, not edged with bristles. Corolla funnel-shaped, 2 to 23⁄4 in. long, scaly on the outside, white sometimes flushed with pink, with an orange or yellow flare in the throat, usually fragrant. Style scaly at least in the lower part. Bot. Mag., n.s., t.1 (as R. taronense).
R. dendricola has its main distribution in northernmost Burma, but extends into Yunnan and perhaps westward into India. It was discovered by Kingdon Ward in the valley of the Nmai Hka (upper Irrawaddy) in 1914, but was introduced by Forrest. The fine clone that received a First Class Certificate (as R. taronense) when shown from Exbury was from F. 27687. Kingdon Ward did, however, send seed later, including three collections from The Triangle of northern Burma in 1953.
The difficulties that the Johnstoneanum and Ciliicalyx aggregates present to the taxonomist are shown by the fact that Dr Sleumer sunk R. dendricola in R. ciliicalyx, while R. taronense, now considered to be conspecific with R. dendricola, was included by him in R. veitchianum.