Shrub, 1–7 m; young shoots brownish, scaly. Leaves 4.8–8.4 × (1.6–)2.4–3.2 cm, broadly elliptic to elliptic, rarely ovate, apex acute, upper surface lacking scales, lower surface with a dense covering of large flat broadly rimmed scales that are 1–2× their own diameter apart. Flowers 3–6, in a dense coalesced compound inflorescence; calyx minute, usually not ciliate; corolla white or pinkish violet, zygomorhic, widely funnel-shaped, 18–22(–25) mm, outer surface lacking scales, glabrous; stamens 10; ovary scaly, impressed below the declinate, usually glabrous style. Flowering May. Royal Horticultural Society (1997)
Distribution China C & S Yunnan, Guizhou
Habitat 840–2,100(–2,600) m
RHS Hardiness Rating H4
Awards AM 1945 (E. de Rothschild, Exbury).
Conservation status Least concern (LC)
Taxonomic note This somewhat tender species differs from the allied R. tatsienense in the form of the leaf scales, and in its coalescing inflorescences. Royal Horticultural Society (1997)
An evergreen shrub 4 to 9 ft high; young wood slightly scaly. Leaves aromatic, oval-lanceolate, tapering about equally to each end, 11⁄2 to 21⁄2 in. long, 3⁄8 to 5⁄8 in. wide, bright green and slightly scaly above, densely scaly beneath, the scales yellowish; stalk 1⁄8 in. long. Flowers produced during May in terminal and axillary clusters of six to eight; pedicels about 3⁄4 in. long, scaly. Calyx minute. Corolla of a pale blush tint with two groups of brown spots on the upper side, up to 11⁄2 in. across, flat, open, short-tubed. Stamens ten, pinkish white, hairy at the base, anthers dark red. Ovary scaly; style glabrous. (s. Triflorum ss. Yunnanense)
Native of Yunnan, S.W. Szechwan, and Kweichow; probably first introduced by Forrest. It belongs to the same group as R. yunnanense, and its flowers are equally pretty. But the leaves are never bristly above, as they often are in R . yunnanense, they are more scaly beneath, the stamens are not so much protruded beyond the corolla as in that species; the flowers are smaller and earlier. It frequently produces a considerable number of flower clusters densely packed at the end of the shoot.
R. siderophyllum received an Award of Merit when shown by Edmund de Rothschild, Exbury, on March 20, 1945.