白毛杜鹃 bai mao du juan

Rhododendron principis Bureau & Franchet var. vellereum (Hutchinson ex Tagg) T. L. Ming.

Small trees, 2–5 m tall; shoots ca. 5 mm in diam., thinly floccose, glabrescent. Petiole 15–20 mm, white-floccose; leaf blade thickly leathery, oblong-elliptic to oblong-lanceolate, 6–12 × 2–4.5 cm; base rounded or cordate; apex obtuse or acute; abaxial surface indumentum silvery-white to gray-yellow, somewhat thick, soft and spongy, surface forming glossy pellicle; adaxial surface glabrous. Inflorescence racemose-umbellate, 10–20-flowered; rachis ca. 10 mm. Pedicel red, 1.5–2 cm, sparsely floccose or glabrescent; calyx lobes 5, ca. 1 mm, shallow, slightly floccose; corolla funnel-campanulate, white, sometimes flushed rose, with purple spots inside, 3.5–4 cm, lobes 5; stamens 10, filaments sparsely puberulent in lower half; ovary ca. 6 × 2.5 mm, 5- or 6-locular, glabrous, sometimes with a few floccose hairs at base; style ca. 2.3 cm, glabrous. Capsule narrowly long-cylindric, sulcate, strongly curved, 23–35 × 4–5 mm, glabrous. Fl. May–Jun, fr. Jul–Sep.

Coniferous forests, Rhododendron thickets, mountains; 3000–4500 m. SE Qinghai, S Xizang.

The types of Rhododendron vellereum and R. principis are very similar, differing only in the indumentum on the ovary. The former taxon may not merit any more than subspecific rank.