An evergreen strongly aromatic shrub 1 to 4 ft high; young shoots densely covered with scales; leaf-bud scales soon falling. Leaves oval or inclined to oblong, tapered about equally to both ends, but with a mucro at the tip, 1⁄2 to 1 in. long, 1⁄4 to 1⁄2 in. wide, dark, rather bright green and somewhat scaly above, thickly covered beneath with reddish scurf; leaf-stalk 1⁄8 in. long. Flowers in a many-flowered, compact, hemispherical truss opening in spring. Calyx 1⁄4 in. long, five-lobed, the lobes unequal in length, sometimes fringed with hairs, finely downy outside. Corolla white, pale yellow, or rose, 3⁄4 in. long, tubular, spreading above into five rounded lobes, downy outside, hairy in the tube. Stamens five, enclosed in the tube, finely downy at the base or glabrous. Ovary scaly, dome-shaped; style very short, stout, glabrous, with a broad flat stigma. (s. Anthopogon)
R. primuliflorum, as interpreted by Cowan and Davidian, is one of the most wide-ranging of rhododendron species, with a disjunct distribution. Its northern area lies in Russia, from E. Siberia east to the Sea of Okhotsk, and in N. Mongolia. South of the Gobi desert its area stretches from the Chinese province of Kansu southward to N.W. Yunnan and westward to E. and S.E. Tibet. It is reported that fossilised peat soils lie beneath the sands of the Gobi desert so the separation of the species into two areas may be of comparatively recent date.
This species was described, as Azalea fragrans, from a specimen collected in Russia near the mouth of the river Lena, and later as Azalea pallida, also from Russia. But neither of these names is valid in Rhododendron, and it was not until 1921 that Rehder provided the name R. adamsii for the Russian plants. But in the meantime Franchet had given the name R. primulaeflorum to a specimen collected in Tibet between Lhasa and Batang and that is therefore the valid name for the species as a whole.
R. primuliflorum (the name is so spelt under modern rules) is represented in gardens by plants raised from seeds collected in W. China and bordering parts of Tibet, where it occurs at altitudes of up to 14,000 ft. It is closely allied to R. cephalanthum but in that species the stamens are sometimes up to eight in number and the bud-scales are persistent. It is rare in cultivation.
var. cephalanthoides (Balf. f. & Forr.) Cowan & Davidian R. cephalanthoides Balf. f. & Forr. – Corolla-tube densely downy outside.