256. Rhododendron williamsianum Rehder & E. H. Wilson in Sargent, Pl. Wilson. 1: 538. 1913.
圆叶杜鹃 yuan ye du juan
Shrubs, 1–2 m tall; older shoots brownish, glabrous; branches slender, 3–5 mm in diam.; young shoots greenish or purplish, with a few glands. Petiole rounded abaxially, flat adaxially, 10–15 mm, sparsely glandular-hairy; leaf blade leathery, broadly ovate or suborbicular, 2.5–5 × 2–4 cm; base cordate or subrounded; apex rounded, with a small cusp; abaxial surface grayish white, with small projections; adaxial surface deep green, glabrous; midrib and lateral veins raised on both surfaces; lateral veins 11–12-paired, veinlets reticulate, obvious abaxially. Inflorescence racemose-umbellate, 2–6-flowered; rachis 5–8 mm, sparsely glandular. Pedicel 2–3 cm, stout, with long-glandular hairs; calyx discoid; lobes 6, 1–2 mm, broadly triangular, outer surface and margin shortly glandular-hairy; corolla broadly campanulate, reddish, 3.5–4 × 4–4.5 cm; lobes 5 or 6, suborbicular, 1–1.5 × ca. 2 cm, emarginate; stamens 10–12(–14), unequal, 1.8–3 cm, filaments glabrous, anthers ovate, deep purple-red; ovary ovate, ca. 5 mm, glandular; style ca. 3.5 cm, nearly equal to corolla, usually glandular, stigma capitate. Capsule cylindric, 15–25 × ca. 6 mm, glandular. Fl. Apr–May, fr. Aug–Sep.
Open forests on mountain slopes, rocks; 1800–2800 m. W Guizhou, SW Sichuan, SE Xizang, NE Yunnan.