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10. Rhododendron subsect. Irrorata (Tagg) Sleumer, Bot. Jahrb. Syst. 74: 548. 1949.

露珠杜鹃亚组 lu zhu du juan ya zu

Fang Mingyuan (方明渊); David F. Chamberlain

Rhododendron subser. Irrorata Tagg in J. B. Stevenson, Sp. Rhodod. 332. 1930 ["Irroratum"].

Shrubs or small trees; young shoots mostly glabrous or glabrescent, occasionally glandular or tomentose. Leaf blade leathery, lanceolate or elliptic-lanceolate; apex acute; abaxial surface usually glabrous when mature, more rarely with a veil of persistent thin indumentum at maturity (R. agastum, R. leptopeplum, and R. tanastylum var. pennivenium). Inflorescence 2–21-flowered; rachis 5–40 mm. Calyx usually reduced to a rim; corolla campanulate or tubular- to open-campanulate, 5-lobed, (7-lobed in R. anthosphaerum), pink, white, yellow or deep crimson, with darker flecks and also sometimes with nectar pouches at the base; stamens 10–14; ovary glabrous, tomentose or glandular-hairy; style glabrous or glandular to tip. Capsule oblong-cylindric, 1–2.5 cm.

About 24 species: Bhutan, China, India, Indonesia (Sumatra), Malaysia, Myanmar, Vietnam; 21 species (14 endemic) in China.

Some species are important horticultural plants in China, e.g., Rhododendron annae and R. irroratum.

1 Abaxial leaf surface with persistent thin indumentum, or at least with hairs on midrib.   (2)
+ Abaxial leaf surface glabrous, though sometimes with sessile punctate glands on midribs and lateral veins.   (9)
2 (1) Leaf blade 13–17(–20.5) cm, adaxial surface with strongly impressed lateral veins, abaxial surface with scattered setose glands.   300 Rhododendron gongshanense
+ Leaf blade never exceeding 15 cm, adaxial surface with at most lightly impressed lateral veins, abaxial surface without setose glands.   (3)
3 (2) Abaxial leaf surface with persistent thin indumentum; ovary tomentose and stipitate-glandular.   (4)
+ Abaxial leaf surface with only midrib hairy, otherwise glabrous.   (5)
4 (3) Leaf blade elliptic or elliptic-lanceolate; style glandular to tip.   299 Rhododendron agastum
+ Leaf blade lanceolate or long-elliptic; style glabrous or glandular only at base.   295 Rhododendron leptopeplum
5 (3) Leaf blade subleathery, lanceolate or oblanceolate, base cuneate; corolla rose.   (6)
+ Leaf blade leathery, lanceolate or long-elliptic, base rounded; corolla yellowish or deep crimson.   (7)
6 (5) Pedicels, ovary, and style glabrous; leaf blade narrowly lanceolate, abaxial surface of midrib with a thin woolly tomentum.   303 Rhododendron araiophyllum
+ Pedicels, ovary, and lower part of style with dense hairs; leaf blade obovate, abaxial surface of midrib with dense brown hairs.   307 Rhododendron pingbianense
7 (5) Pedicel and ovary glabrous; leaf blade 3–4.5 cm wide, abaxial surface of midrib with brown hairs; corolla deep crimson.   301 Rhododendron ramsdenianum
+ Pedicel and ovary densely hairy; leaf blade 1.5–3.5 cm wide, abaxial surface of midrib thinly rufous tomentose or stellate-tomentose; corolla yellowish or purplish.   (8)
8 (7) Leaf blade 1.5–2.5 cm wide, abaxial surface of midrib thinly tomentose, base symmetrical; corolla yellowish.   308 Rhododendron laojunshanense
+ Leaf blade 2.5–3.5 cm wide, abaxial surface of midrib stellate-tomentose, base asymmetrical; corolla purplish with purple blotch and flecks.   310 Rhododendron sikangense
9 (1) Ovary eglandular, tomentose or glabrous; style usually glabrous, rarely tomentose at base.   (10)
+ Ovary glandular, or glandular-setose and tomentose; style glandular or glabrous.   (15)
10 (9) Calyx usually ca. 10 mm; ovary and style base tomentose.   312 Rhododendron dimitrum
+ Calyx 1–3 mm; ovary and style usually glabrous or puberulent.   (11)
11 (10) Leaves subleathery, lanceolate or oblanceolate, apex obtuse or acute; corolla 6–7-lobed.   292 Rhododendron anthosphaerum
+ Leaf blade leathery; apex acute; corolla 5-lobed.   (12)
12 (11) Rachis stout, 5–20 mm, glabrous; inflorescence 5–10-flowered.   (13)
+ Rachis slender, 15–35 mm, tomentose; inflorescence usually 8–15-flowered.   (14)
13 (12) Rachis 0.5–1 cm; corolla fleshy, deep crimson; leaves elliptic-lanceolate.   293 Rhododendron tanastylum
+ Rachis 1.5–2 cm; corolla not fleshy, purplish crimson; leaves oblanceolate.   297 Rhododendron spanotrichum
14 (12) Ovary strigose; leaves lanceolate or elliptic-lanceolate, adaxial surface not wax-coated.   302 Rhododendron kendrickii
+ Ovary glabrous; leaves oblanceolate, adaxial surface usually wax-coated.   294 Rhododendron lukiangense
15 (9) Ovary glandular or glandular-setose; style glabrous or glandular only in lower half.   (16)
+ Ovary glandular; style glandular to tip.   (18)
16 (15) Leaf blade long-elliptic or obovate-elliptic, 8–13 cm; apex obtuse or rounded; corolla 4.5–5 cm; pedicel and ovary with dense dendritic hairs; calyx lobes rounded, ca. 3 × 4 mm.   296 Rhododendron papillatum
+ Leaf blade elliptic-lanceolate or ovate-lanceolate, 5–10 cm, apex cuspidate; corolla 2.5–4 cm; pedicel and ovary without dendritic hairs; calyx 1–3.5 mm.   (17)
17 (16) Ovary and lower part of style glandular-hairy; pedicel glandular-setose.   309 Rhododendron brevinerve
+ Ovary glandular-setose; style glabrous; pedicel sparsely stipitate-glandular.   306 Rhododendron guizhouense
18 (15) Corolla tubular-campanulate, reddish purple; leaves narrowly lanceolate, 8–17 × 2–3 cm; petiole and pedicel densely glandular-setose.   311 Rhododendron mengtszense
+ Corolla campanulate or open-campanulate; leaves lanceolate to elliptic-lanceolate, not more than 12 cm; petiole and pedicel glabrous.   (19)
19 (18) Corolla campanulate, 3.5–5 cm, white to yellow.   298 Rhododendron irroratum
+ Corolla open-campanulate or cup-shaped, 2–3(–4) cm, white or rose.   (20)
20 (19) Leaf blade thick, leathery, 2.5–5 cm.   304 Rhododendron aberconwayi
+ Leaf blade subleathery, 7–10 cm.   305 Rhododendron annae

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