A dwarf evergreen shrub 6 to 12 in. high, of close, bushy habit; young shoots densely clothed with pale bristles and minute down. Leaves oblong, tapered at the base, rounded at the apex, 3⁄8 to 5⁄8 in. long, bristly on the margins, very scaly above, rather glaucous and less scaly beneath. Flowers three to eight in a terminal cluster; pedicels scaly, slender, about 1⁄4 in. long. Calyx comparatively large, scaly and downy, divided almost to the base into five ovate lobes about 1⁄4 in. long. Corolla about 1 in. across, reddish purple, lobed to two-thirds of its depth. Stamens ten, hairy at the base. Ovary scaly; style glabrous. Bot. Mag., t. 8523.
Native of the Himalaya as far west as Kumaon; introduced in 1825. It is an alpine rhododendron, found at altitudes of up to 16,000 ft. 'It is the Tsallu of the Sikkim Bhoteas and Tibetans, who attribute the oppression and headaches attending the crossing of the loftiest passes of Eastern Himalaya to the strongly resinous odour of this and of R. anthopogon, Wall. (Palu of the natives). The species certainly abounds near the summits of all the passes, and after hot sunshine fills the atmosphere with its powerful aroma, far too heavy to be agreeable, and greatly aggravating the discomforts of toiling in the rarefied medium of these elevations' (Hooker).
R. setosum is at present placed in the Lapponicum series, though its deeply lobed corolla, large calyx, and bristly stems are not in keeping with that series. It is an interesting species, with brightly coloured flowers, but is difficult to cultivate successfully in southern England, where it misses its winter covering of snow and is often excited into growth too early.
From the Supplement (Vol. V)
It was mentioned in the last paragraph (page 769) that this is out of place in the Lapponicum series. It is, however, retained in subsect. Lapponica in the Edinburgh revision, as an aberrant member.