An evergreen shrub or small tree, up to 40 ft high in the wild; young stems clad with whitish or grey wool. Leaves oblong, oblong-lanceolate, or oblong-oblanceolate, 6 to 10 in. long, 11⁄2 to 3 in. wide, obtuse, rounded or sometimes cuspidate at the apex, cuneate to rounded at the base, lateral veins impressed, glabrous above when mature, clad beneath with a dense whitish or grey felt; petiole up to 7⁄8 in, long, woolly. Inflorescence a dense terminal truss of up to forty or so flowers, opening late February to April; pedicels 3⁄8 to 5⁄8 in. long. Calyx 1⁄8 in. or slightly less long. Corolla campanulate or tubular-campanulate, about 2 in. wide, carmine or rosy purple, five-lobed. Stamens ten. Ovary clad with grey or white wool; style glabrous. (s. and ss. Arboreum)
R. lanigerum was described in 1931 from a specimen collected by Kingdon Ward in 1928 in the Delei valley, Mishmi Hills, Assam (KW 8251), growing with other big-leaved rhododendrons at 10,000-11,000 ft. He collected seed, and all the plants known as R. lanigerum up to about 1960 are from this number. However, as it has later proved, Kingdon Ward had found R. lanigerum earlier, in 1924, growing in Pemako on the southern side of the Doshong La, at the eastern end of the Himalaya, at 9,000-10,000 ft. He collected seed but never saw the plants in flower, and his fruiting specimen was at first taken to be R. niveum (KW 6258). It was described as a new species in 1936, under the name R. silvaticum, the details of the flowers and inflorescence being taken from a plant at Muncaster Castle, raised from KW 6258. The two species were placed in different series – R. lanigerum in s. Falconeri, as an aberrant member, and R. silvaticum in ss. Arboreum. So it remained until about 1961, when exhibits at the early R.H.S. shows under the name R. silvaticum were pronounced to be R. lanigerum, of which R. silvaticum appears as a synonym in the R.H.S. Handbook, 1963 (and in later editions). R. lanigerum (silvaticum) was also found by Kingdon Ward in the Tsangpo Gorge, where seed was later collected by Ludlow, Sherriff, and Elliot (no. 13591, from Pemakochung).
R. lanigerum, at its best, is a splendid species, with beautifully coloured flowers in noble trusses, but the numerous awards given to it are a testimony more to its variability than to its worth as a garden plant, since it flowers too early in the spring to be reliable in its display. The type-introduction (KW 8251) seems to be uncommon, and is said to be rather tender. It received an Award of Merit on March 29, 1949, when shown by Col. E. Bolitho, Trengwainton, Cornwall (flowers carmine). The other awards have all been given to forms exhibited as R. silvaticum (or originally grown under that name). These are: ‘Round Wood’, A.M. March 20, 1951, shown by Crown Estate Commissioners, Windsor, and Mrs Stevenson (flowers crimson, twenty in the truss); ‘Silvia’, A.M. April 13, 1954, shown by R. Olaf Hambro, Logan House, Stranraer (flowers pale crimson suffused white, forty in the truss; R.C.Y.B. 1955, frontispiece); ‘Stonehurst’, A.M. March 14, 1961, shown by Ralph Strauss, Stonehurst, Ardingly (flowers cherry-red; R.C.Y.B. 1962, fig. 29); ‘Chapel Wood’, F.C.C. February 21, 1967, and previously an A.M. February 28, 1961, shown by the Crown Estate Commissioners, Windsor (flowers Neyron Rose, forty to fifty in the truss; R.C.Y.B. 1962, fig. 27).