An evergreen shrub up to 10 ft high; branchlets slender, usually glandular, hairy or glabrous. Leaves oblong to oval or obovate, 1 to 31⁄2 in. long, 1⁄2 to 11⁄2 in. wide, rounded or obtuse at both ends, or sometimes slightly cordate at the base, dark green and glabrous or almost so above, underside paler and sometimes slightly glaucous, glabrous, or sometimes with a thin coating of hairs which often wears off by late summer; petiole up to 11⁄8 in. long. Flowers in terminal clusters of four to eight, opening in April or May; pedicels up to 11⁄8 in. long, glandular and sometimes hairy. Calyx up to 1⁄4 in. long, more or less glandular, sometimes hairy on the margin. Corolla between funnel-shaped and bell-shaped, 11⁄2 to 13⁄4 in. long and wide, five-lobed, varying in colour from white to various shades of rose, usually unspotted, but often with a crimson blotch at the base. Ovary densely glandular, sometimes slightly hairy also; style glabrous, sometimes slightly glandular at the base. (s. Thomsonii ss. Selense)
Native of N.W. Yunnan, bordering parts of S.E. Tibet, and of S.W. Szechwan; discovered by the French missionary Soulié on the Se La, Mekong-Salween divide, in 1895; introduced by Forrest from the same area in 1917. It is a somewhat variable species in shape and size of leaf, degree of glandularity, flower-colour, etc., and numerous species, now included in R. selense, were made out of its fluctuations. It is one of those species that is rarely seen in cultivation outside the gardens where it was raised from the wild seed. Growing by the thousand on its native mountainsides it must be a lovely sight when in flower, but the individual plant makes little display and is very slow to reach flowering age.
The following varieties are retained by Cowan and Davidian in their revision of the Thomsonii series;
var. duseimatum (Balf. f. & Forr.) Cowan & Davidian R. duseimatum Balf. f. & Forr. – Ovary tomentose. Leaves oblong-lanceloate, 3 to 4 in. long.
var. pagophilum (Balf. f. & Ward) Cowan & Davidian R. pagophilum Balf. f. & Ward – This name is retained by Cowan and Davidian for plants with small elliptic leaves and small flowers (usually dark rose to crimson in colour). In the type, the leaves were about 2 in. long and 11⁄8 in. wide.
var. probum (Balf. f. & Forr.) Cowan & Davidian R. probum Balf. f. & Forr. – A form with white, unmarked flowers.
R. dasycladum Balf. f. & W. W. Sm. R. rhaibocarpum Balf. f. & W. W. Sm. – This is nearly related to R. selense, but the young shoots and petioles are very bristly-glandular. The corolla is white, rose, or lilac-pink, with a crimson blotch at the base. It is usually a tall shrub in cultivation, and flowers quite freely. The deeper-coloured forms are attractive. It occurs wild within the area of R. selense.
R. setiferum Balf. f. & Forr. – Near to R. dasycladum, and with the same bristly-glandular branchlets and petioles, but with thick, leathery leaves. It was introduced by Forrest under F.14006 from the Salween-Mekong divide. The flowers are white, with crimson markings at the base.
From the Supplement (Vol. V)
The vars. pagophilum and probum are included in the typical subspecies of R. selense by Dr Chamberlain, while var. duseimatum is transferred to R. calvescens (not treated in the main work and probably not in cultivation).
subsp. dasycladum (Balf.f. & W.W. SM.) Chamberlain – Mentioned under R. selense on page 767 as a related species. Differing from subsp. selense in the young growths bearing long-stalked glands or glandular bristles, and longer calyx-lobes.
subsp. setiferum Balf.f. & Forr.) Chamberlain – Also mentioned under R. selense as a species. A character not mentioned is that the leaves have a more or less persistent though discontinuous indumentum beneath. Possibly a natural hybrid between R. selense subsp. selense and R. bainbridgeanum. (Rev. 2, p. 280).
subsp. jucundum (Balf.f. & W.W. Sm.) Chamberlain R. jucundum Balf.f. & W.W. Sm. – See Rev. 2, p. 280. Rare in cultivation and not mentioned in the main work.
R. × erythrocalyx Balf.f. & Forr. (as species) – This is considered by Dr Chamberlain to be a natural hybrid between R. selense and R. wardii, making swarms where the two species are in contact. Four of Balfour's species founded on Forrest collections are here included in synonymy. A fifth – R. panteumorphum – mentioned under R. camplyocarpum on page 620, may also belong here (Rev. 2, pp. 280-81).