《中国植物志》|| 杜鹃花科 ERICACEAE ||树形杜鹃亚组 Subsect. Arborea Sleumer ||树形杜鹃 Rhododendron arboreum Sm.

129. 树形杜鹃（中国高等植物图鉴）
Rhododendron arboreum Smith in Exot. Bot. 1: 9. t. 6. 1805; Tagg in Stevenson, Spec. Rhodod. 14. 1930;中国高等植物图鉴3: 88. 图4130. 1974; Cullen et Chamb. in Not. Bot. Gard. Edinb. 37: 328. 1979; Chamb. in Not. Bot. Gard. Edinb. 39: 328. 1982. ——R. puniceum Roxb. in Fl. Brit. India. 2: 409. 1832. ——R. windsorii Nutt. in Hooker's Journ. Bot. Kew Gard. Misc. 5: 357. 1853; 西藏植物志3: 575. 图232. 1-5. 1986.
常绿乔木，高3-5米；从基部分枝；树皮灰褐色，片状剥落；幼枝粗壮，密被灰色绒毛，在花序下的小枝直径3.5-6毫米；老枝绿色，无毛，有明显的叶痕。冬芽卵圆形，长1-1.2厘米，直径5-6毫米，略被灰色短柔毛。叶革质，长圆状披针形或长圆状倒披针形，长6-15.5厘米，宽2-4.2厘米，先端钝或短渐尖，基部楔形或近于圆形，边缘反卷，上面鲜绿色，后变为无毛，下面银白色，被有一层紧密的灰白色至黄褐色薄毛被，薄膜状有时稍增厚，中脉在上面凹下，下面凸起，近于无毛，侧脉15-26对；叶柄长1-2.5厘米，幼时密被黄褐色绒毛和少数腺体，老时有毛被残迹。顶生总状伞形花序，有花约20朵，紧密；总轴长约1-1.5厘米，密被绒毛；花梗长9毫米，密被黄褐色绒毛和腺体；花萼小，长1.5-2毫米，外面具绒毛，有5枚齿状裂片，边缘有纤毛；花冠管状钟形，长3.5厘米，宽3.8厘米，肉质，紫红色至深血红色，内面基部有5枚深色的蜜腺囊，中部一侧有紫色斑点，裂片5，扁圆形，长1.2厘米，宽1.7厘米，顶端有深缺刻；雄蕊10，不等长，长1.7-2.7厘米，花丝无毛，花药长圆形，长1-2.5毫米；子房圆锥形，长4.6毫米，密被淡黄褐色绒毛和腺体；花柱长3.3厘米，无毛，柱头头状，宽约2.5毫米。蒴果长圆状圆柱形，长约2厘米，直或微弯曲，有绒毛及腺体残迹。花期5月，果期8月。
产贵州西部和西藏南部。生于海拔1 500-3 550米的溪谷林下或栎林中。克什米尔地区、尼泊尔、锡金、不丹、印度东北部、缅甸及斯里兰卡也有分布。藏名“打马”，花作药用，有治咳止喘的功效。

《Flora of China》|| Apiaceae || Rhododendron ||树形杜鹃 Rhododendron arboreum

336. Rhododendron arboreum Smith, Exot. Bot. 1: 9. 1805.

树形杜鹃 shu xing du juan

Trees, usually evergreen, (1–)5–20(–30) m tall; trunk well-defined; bark gray-brownish, exfoliating into thin and small irregular flakes; young shoots stout, with distinct leaf traces, densely grayish tomentose, glabrescent. Winter buds ovoid, 10–12 × 5–6 mm, puberulent. Petiole 10–25 mm with dense fawn indumentum intermixed with glands, sometimes glabrescent; leaf blade leathery, oblong-lanceolate or oblong-oblanceolate, 6–15 × 2–4.5 cm; base cuneate or ± rounded; margin revolute; apex acuminate or acute; abaxial surface with indumentum 1- or 2-layered, densely compacted, white to fawn tomentose, sometimes with loosely floccose brown upper layer, hairs dendroid, glabrescent; adaxial surface reticulate to bullate, glabrous; midrib deeply impressed adaxially; lateral veins 15–26-paired. Inflorescence dense, ca. 20-flowered, rachis 10–15 mm, tomentose. Pedicel ca. 0.9 cm, pilose, glandular; calyx lobes 5, 1–2 mm, small, triangular, sparsely glandular and hairy; corolla tubular-campanulate, pink to deeply crimson, rarely white, 3.5–4 cm, with 5 black-blotched basal nectar pouches and dark flecks; lobes 5, 1.2–1.7 cm, apex emarginate; stamens 10, unequal, 1.7–2.7 cm, filaments glabrous; ovary conoid, 4–6 mm, white-tomentose, sometimes also glandular; style ca. 3.3 cm, glabrous. Capsule cylindric, ca. 30 × 6 mm. Fl. May, fr. Aug.

Three varieties occur in China. The name used in Xizang, “da ma” (打马), refers to the medicinal use of the flowers in treating coughs.

Forests, thickets, slopes; 1500–3800 m. ?W Guizhou, S Xizang [Bhutan, N India, Kashmir, Nepal, Sikkim, Sri Lanka, N Thailand, N Vietnam].