An evergreen, erect-branched shrub described as growing up to 3 ft high in the wild, but sometimes taller in cultivation; young shoots rough with scales. Leaves elliptic, up to 3⁄4 in. long, about half as wide, slightly glaucous green and thickly set with shining yellow scales above, more sparsely scaly beneath; stalk about 1⁄8 in. long. Flowers usually solitary, with a very short scaly stalk. Calyx shorter than the corolla-tube, deeply five-lobed, the lobes blunt, oval-oblong, sparsely scaly, usually fringed with weak hairs. Corolla about 1 in. wide, purple or blue-purple, with or without scales on the outside, hairy in the throat. Stamens seven or eight, with purple filaments; anthers yellowish. Ovary densely scaly; style purple, glabrous. (s. Lapponicum)
Native of W. Szechwan; discovered by Wilson in 1908 at altitudes of 10,000 ft and upwards. It is a very hardy species, allied to R. impeditum, but taller and not flowering until May. Forms with the corolla not scaly outside would in fact run down to R. impeditum in the key in Species of Rhododendron, which is badly out-of-date. R. verruculosum received an Award of Merit when shown by Col. S. R. Clarke, Borde Hill, Sussex, on May 24, 1932.
From the Supplement (Vol. V)
The Philipsons consider that R. verruculosum is a natural hybrid of R. flavidum, the other parent of which is uncertain. This judgement, however, applies only to the type-specimen, collected by Wilson in flower during his first expedition for the Arnold Arboretum. No seed-sending by Wilson was ever identified as R. verruculosum, and it is uncertain how the garden plants originated. The most likely possibility is that they occurred as rogues among seedlings of R. flavidum raised by Veitch from Wilson's sendings and distributed at the winding-up sale of the Coombe Wood nursery.