显萼杜鹃 xian e du juan

Rhododendron beimaense I. B. Balfour & Forrest; R. cymbomorphum I. B. Balfour & Forrest; R. erythrocalyx subsp. beimaense (I. B. Balfour & Forrest) Tagg; R. erythrocalyx subsp. docimum I. B. Balfour ex Tagg; R. erythrocalyx subsp. eucallum (I. B. Balfour & Forrest) Tagg; R. erythrocalyx subsp. truncatulum (I. B. Balfour & Forrest) Tagg; R. eucallum I. B. Balfour & Forrest; ?R. panteumorphum I. B. Balfour & W. W. Smith; R. truncatulum I. B. Balfour & Forrest.

Shrubs, 2–3 m tall; old branches grayish white, smooth, sometimes with bark flaking; young branches glandular-hairy. Petiole terete, 10–15 mm, glabrous; leaf blade leathery, ovate-elliptic or oblong-elliptic, 6–8 × 2.5–4 cm; base rounded or subcordate, usually asymmetrical; margin thin, usually revolute; apex mucronate; both surfaces glabrous; abaxial surface grayish white; adaxial surface deep green; midrib raised abaxially, flat adaxially; lateral veins 15–18-paired, visible adaxially, inconspicuous abaxially. Inflorescence racemose-umbellate, 3–7-flowered; rachis ca. 3 mm, glabrous. Pedicel slender, 2–3 cm, sparsely glandular, glabrous; calyx lobes 5, large, ovate, outside nearly glabrous, margin glandular, 4–7 × ca. 4 mm; corolla funnelform-campanulate, milky-white or pink, rarely yellowish, 3.5–4 × ca. 4 cm; lobes 5, suborbicular, ca. 1.5 × 2 cm, apex emarginate; stamens 10, unequal, 1.2–2.5 cm, filaments glabrous, anthers large, oblong, ca. 3 mm; ovary cylindric, ca. 5 mm, densely glandular; style ca. 2.5 cm, nearly equal to corolla, lower part glandular, stigma slightly expanded. Capsule slender, cylindric, curved, ca. 2 × 0.5 mm, with short glandular hairs. Fl. May–Jun, fr. Aug–Oct.

Coniferous forests, Rhododendron thickets; 3000–3900 m. E Xizang, NW Yunnan.

Field observations on Baima Shan in NW Yunnan, the type locality of Rhododendron ×erythrocalyx and several of the cited synonyms, indicate that this entity is a hybrid between R. selense and R. wardii. It is intermediate between, and occurs in mixed populations with, both parents.

If Rhododendron panteumorphum is indeed a synonym of R. ×erythrocalyx, then the former name would have priority (I. B. Balfour & W. W. Smith, Notes Roy. Bot. Gard. Edinburgh 9: 257. 1916).