A moderately compact shrub up to 3 ft high. Leaves oblong-elliptic to oblong- lanceolate, about 3⁄8 in. long in the type, but up to 5⁄8 in. long in some cultivated plants, margins often recurved, upper surface glaucous green, sea-green or deep steely blue, conspicuously dotted with scales, undersides papillose and whitish between the scales, which are opaque, uniform, spaced less than their own diameter apart, sometimes contiguous or even overlapping; petiole very short. Inflorescence terminal, composed of three to five very short-stalked flowers, produced in April or May. Calyx well developed, about as long as the corolla-tube, deeply lobed, scaly outside and fringed with weak hairs. Corolla 3⁄4 to 1 in. wide, in some shade of purple or blue-purple, widely funnel-shaped to almost rotate, with a short tube, hairy inside at the base. Filaments of stamens hairy. Style equalling the stamens or longer, glabrous. (s. Lapponicum)
Native of Yunnan, China; discovered by Père Delavay in the Tali range and described in 1885; introduced by Forrest from the same area in 1906. According to him, it occurs there on cliff-ledges in pine forests on the eastern (drier) side of the range and is the dominant species on the Sungkwei pass some 50 miles north of Tali. It is variable in the colour of its flowers and also in the degree of glaucousness of its foliage, though the leaves are always glaucous when young. In some plants (usually grown as R. impeditum), the leaves remain sea-green or dark blue-green throughout the winter, and are then more decorative than most members of the series. The habit is also variable, some forms being dwarf and slow growing, others more robust and open. The specific epithet refers to the straightness and dense arrangement of the branchlets on the type-specimen, not to the habit of the plant as a whole.
R. fastigiatum received an Award of Merit when shown by Messrs Reuthe in 1914.
R. impeditum Balf. f. R. fastigiatum of the 1st edition of this work, not Franch.; R. semanteum Balf. f., nom. inedit. – This species was discovered by Forrest on the eastern and western flanks of the Lichiang range, Yunnan, in 1910, and was introduced by him in that year. It was at first considered to be R. fastigiatum, and went into cultivation under that name, but was described as a new species in 1916. Balfour wrote: 'Like that plant [R. fastigiatum] in its cushion habit its foliage is very different, and one can distinguish the two plants at a glance. Rh. fastigiatum has a grey hoary appearance, Rh. impeditum dark green. Both the plants have discontiguous under-leaf scales, but whilst in Rh. fastigiatum the bare intervals of epidermis are greyish, often tinted slightly red, in Rh. impeditum the epidermis is mat green.' This difference in leaf-colouring is especially noticeable in the young growths, and there is the further difference that in R. fastigiatum the scales on the blade beneath, seen under low magnification, are opaque, waxy and very solid in appearance, whilst those of R. impeditum are light brown and lustrous. But on year-old leaves of R. fastigiatum a few of the scales have lost their wax, and even on younger leaves the scales on the midrib beneath are like those of R. impeditum. Other distinctions are that the flowers are usually not more than three per truss and are mauve rather than purple. But the key-character relied on by Balfour – outside of corolla scaly in R. fastigiatum, not so in R. impeditum – does not hold good. There is no constant difference in size or shape of leaf.
R. impeditum is not common in commerce, but is available from specialist nurseries (this, of course, applies to the true species, not to R. fastigiatum masquerading as R. impeditum). It received an Award of Merit in 1944 when shown by the Sunningdale Nurseries, who raised it from Rock 59263, collected in the type-area. Earlier, the same award had been given to a plant from seed of F.20492, collected in the Muli area of S.W. Szechwan and distributed under the unpublished name R. semanteum. No example of this form has been seen, but the name R. semanteum is given as a synonym of R. impeditum by Hutchinson in Species of Rhododendron.
R. litangense Balf. f. ex Hutch. – This is near to R. impeditum, but cultivated plants under the name differ from the dwarf compact form of R. impeditum in their more erect habit and their darker leaves and flowers.
From the Supplement (Vol. V)
R. impeditum – R. litangense, mentioned under this species, is included in it by the Philipsons, with the result that R. impeditum, although typically of low and compact habit, now includes plants growing to about 4 ft high. This merger removes one more difference between R. impeditum and R. fastigiatum, which can be either mound-forming or erect. We are left with no reliable differential character other than that in R. impeditum the leaves at all stages of growth are green, with light brown scales on the undersides (see further on pages 658-9). This is hardly enough to justify species rank for R. impeditum, especially as plants identified as belonging to it occur in the same localities as R. fastigiatum.
In Plantae Wilsonianae (Vol. I, p. 507) it is stated that Wilson found R. fastigiatum in moorlands around Tachien-lu (Kangding) in western Szechwan. In fact this rhododendron belongs to the recently described R. minyaense, for which see in this supplement under R. websterianum.