An evergreen shrub 3 to 9 ft high of stiff habit; young shoots clothed with loose and (at first) white wool and glandular bristles. Leaves lanceolate or narrowly elliptic, sharply pointed, 2 to 4 in. long, 1⁄2 to 11⁄4 in wide, dark green and becoming glabrous above, covered beneath with a thick loose wool which is at first dull white, later reddish brown, and persists till the leaf falls; stalk 1⁄4 to 1⁄2 in. long, woolly and glandular like the young shoot. Flowers in a terminal hemispherical truss 3 in. wide, opening in May. Calyx small, shallowly five-lobed, glandular; flower-stalk 5⁄8 in. long, woolly and glandular. Corolla bell-shaped, clear scarlet, about 11⁄2 in. long and wide, five-lobed. Stamens ten, 1 to 11⁄2 in. long, glabrous. Ovary slender, tapered, thickly clothed like the lower part of the style with glandular hairs. Bot. Mag., t. 9301. (s. and ss. Neriiflorum)
R. sperabile was discovered by Farrer and Cox in 1919, growing at 10,000 ft in a ravine below the Hpimaw pass in north-east Upper Burma and was introduced by them (Farrer 888); later sendings by Forrest were from the same area. According to the collectors' field notes it varies in the colour of its flowers from scarlet-crimson to deep crimson, and also in habit, from compact to leggy, but is always comparatively dwarf, and this is also true of cultivated plants, which are normally less than 6 ft high.
R. sperabile is hardy in the woodland gardens of Sussex and flowers freely. It is not so fine a species as R. neriiflorum, but the dwarfest and most compact forms deserve to be propagated. It received an Award of Merit when shown by Lionel de Rothschild, Exbury, on May 5, 1925 (from Farrer 888).
A vigorous and tall-growing form of R. sperabile was introduced by Kingdon Ward in 1926 from the Di Chu valley on the borders between Assam, Tibet, and Burma (KW 7124).
var. weihsiense Tagg & Forr. – Leaves relatively narrower, less lanceolate, sometimes elongate elliptic, with a paler and thinner indumentum. Introduced by Forrest from the Mekong-Salween divide west of Weihsi. It grows taller than the typical form and is of rather sparse habit. The name var. chimiliense was given to Forrest's 26478, from the Chimi-li pass on the Nmai-Salween divide, but the name was apparently never published. In some of the cultivated plants from this batch of seed the leaves are almost glabrous beneath.
R. sperabilioides Tagg & Forr. – Resembling the above in general appearance this differs in having no glands on the ovary, leaf-stalk, and young shoots. The stamens also are hairy at the base. Flowers of various shades of crimson, borne in trusses of six to ten flowers, the corolla 1 to 11⁄2 in long. A native of the Tsarong region of S.E. Tibet on the Salween-Kiuchiang divide; discovered by Forrest and introduced by him in 1921. It occurs at higher altitudes than R. sperabile – 12,000 to 13,000 ft – and is always of dwarf habit in cultivation, to about 4 ft high. It received an Award of Merit on April 4, 1933, when shown from Exbury.