450. Rhododendron thomsonii J. D. Hooker, Rhododendr. Sikkim-Himalaya. 2: t. 12. 1851 [“thomsoni”].
半圆叶杜鹃 ban yuan ye du juan
Shrubs or small trees, 2–4 m tall; older branches pale gray-brown; bark exfoliating in flakes; young shoots greenish, glabrous. Petiole slender, 10–30 × ca. 2 mm, glabrous; leaf blade leathery, oblong-elliptic to ovate or orbicular to obovate, 3–7 × 2–6 cm; base rounded to cordate; margin reflexed; apex rounded, apiculate; abaxial surface glaucous, papillate, with some red glandular hairs, sometimes sparsely hairy; adaxial surface dark green, smooth, glabrous; midrib prominent and raised abaxially, flat adaxially; lateral veins 13–14-paired, conspicuous. Inflorescence racemose-umbellate, 4–8-flowered; rachis 5–12 mm, glabrous. Pedicel 1–2 cm, usually glabrous; calyx with upper half tinged red, lower half green, cupular to irregularly split; lobes 5, 2–12 mm, rounded or truncate, glabrous; corolla campanulate, deep crimson, 4–5 cm, fleshy, lobes 5, suborbicular, ca. 1 × 1.5 cm, emarginate; stamens 10, unequal, 2–3 cm; ovary conoid-cylindric, 5–7 mm, glabrous or glandular-hairy; style 3–3.5 cm, glabrous or densely glandular-hairy; stigma slightly swollen. Capsule oblong, 12–15 × 5–8 mm, glabrous, calyx persistent. Fl. Jun.
Mixed forests, thickets, rocky slopes; 3000–4000 m. S Xizang [Bhutan, N India, Nepal, Sikkim].