A dwarf evergreen shrub 2 to 4 ft high, with obovate or oblong leaves tapering to the base, 11⁄2 to 31⁄2 in. long, 1⁄2 to 11⁄2 in. wide, densely clothed beneath with loose tawny wool. Flowers opening in April or early May in clusters of six to eight; stalks clad with tawny bristles. Calyx variable in size. Corolla typically clear, unspotted, lemon-yellow, but sometimes rose-coloured, or in intermediate shades, bell-shaped, 13⁄4 in. long, five-lobed. Stamens ten, downy at the base or glabrous. Ovary matted with tawny hairs and glandular bristly; style glabrous. (s. Neriiflorum ss. Sanguineum)
This variable species resembles R. sanguineum in the shape and texture of its leaves, but they differ markedly in their thick indumentum of matted hairs. It was described from specimens collected by Forrest on the Mekong-Salween divide, N.W. Yunnan, and introduced by him. Although the flowers were said in the original description to be lemon-yellow, the authors cite Forrest's 14271, in which the flowers were described in the field note as 'soft rose without markings'. The species also occurs in S.E. Tibet (Tsarong) on the Salween-Irrawaddy divide.
The following subspecies are placed under R. citriniflorum by Cowan (Notes R.B.G. Edin., Vol. 20, p. 75).
subsp. aureolum Cowan – Ovary without glands. Otherwise not differing from the type.
subsp. horaeum (Balf. f. & Forr.) Cowan R. horaeum Balf. f. & Forr. – Resembling the type in foliage, but flowers deep crimson. Ovary tomentose, without glands. Introduced by Forrest from S.E. Tibet (Tsarong), later by Rock. The subsp. rubens Cowan is the same, but the ovary is glandular as well as tomentose.
From the Supplement (Vol. V)
Dr Chamberlain provides a simpler treatment than Dr Cowan's, recognising only one variety (not subspecies).
var. horaeum (Balf.f. & Forr.) Chamberlain R. horaeum Balf.f. & Forr.; R. citriniflorum subsp. horaeum (Balf.f. & Forr.) Cowan; R. c. subsp. aureolum Cowan – Flowers red or orange or in intermediate shades; calyx mostly 1⁄4 to 1⁄2 in. long; ovary and pedicels without glands (against flowers yellow, calyx shorter, ovary and pedicels usually glandular in the typical variety). However, Dr Chamberlain admits that intermediates occur, Cowan's R. c. subsp. rubens being of this nature.
For natural hybrids, see Rev. 2., p. 393.