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FOC | Family List | FOC Vol. 14 | Ericaceae

5. Rhododendron subg. Hymenanthes (Blume) K. Koch, Dendrologie. 2(1): 170. 1872 [“Hymenanthus”].

常绿杜鹃亚属 chang lü du juan ya shu

Hymenanthes Blume, Bijdr. 862. 1826.

Shrubs or trees, rarely small creeping shrubs, evergreen; new leafy shoots from lateral buds, i.e., from axils of leaves of previous season; young shoots setose, glandular-hairy, or glabrous, not scaly. Leaves large; leaf blade leathery, narrowly elliptic to broadly lanceolate or suborbicular; abaxial surface glabrous or hairy, rarely glandular or waxy above, not scaly. Inflorescence terminal, umbellate-racemose, many-flowered, rarely 1- or 2-flowered. Calyx small, green or red, rim-like, rarely enlarged into a cup, 5(–8)-lobed; corolla campanulate or funnelform, rarely ± tubular, lobes 5–8, pinkish red, white or red to purplish red, rarely yellow, sometimes with darker nectar pouches at base; stamens 10(–20), usually twice as many as corolla lobes, unequal; ovary 5–18-locular, glabrous, hairy, or glandular; style slender, long, glabrous or hairy or glandular at apex. Capsule cylindric, straight to curved, glabrous or not, valves opening when mature. Seeds often with a thin membranous wing.

About 270 species: mostly in Asia, also in Europe and North America; 259 species (190 endemic) in China.

1 Young branches and petioles generally setose or with stipitate to setose glands.   (2)
+ Young branches glabrous, rarely pilose or with glands, without bristles, never setose.   (11)
2 (1) Corolla 7-lobed; stamens 14–16.   2 Rhododendron subsect. Auriculata
+ Corolla 5–6-lobed; stamens 10–14.   (3)
3 (2) Corolla tube densely hairy outside.   18 Rhododendron subsect. Griersoniana
+ Corolla tube glabrous outside.   (4)
4 (3) Corolla campanulate or funnelform, yellow or white to red or purplish red, without basal nectar pouches.   (5)
+ Corolla tubular, often deep red, with nectar pouches at base.   (7)
5 (4) Leaf apex acute; abaxial surface stipitate-glandular, lanate or strigose.   9 Rhododendron subsect. Glischra
+ Leaf apex rounded; abaxial surface glabrous.   (6)
6 (5) Corolla broadly campanulate, style with glands throughout.   5 Rhododendron subsect. Williamsiana
+ Corolla funnelform, narrow; style glabrous.   8 Rhododendron subsect. Selensia
7 (4) Peduncle to 4 cm; style glandular or stellate-hairy.   19 Rhododendron subsect. Parishia
+ Peduncle to 1 cm; style glabrous or glandular only at base.   (8)
8 (7) Inflorescence 2–8(–12)-flowered; leaf apex acute or rounded.   21 Rhododendron subsect. Neriiflora
+ Inflorescence usually 7–20-flowered; leaf apex cuspidate.   (9)
9 (8) Leaves lanceolate to elliptic; capsule curved.   10 Rhododendron subsect. Irrorata
+ Leaves ovate to elliptic; capsule straight.   (10)
10 (9) Leaf apex cuspidate.   7 Rhododendron subsect. Maculifera
+ Leaf apex acute to rounded at apex.   20 Rhododendron subsect. Barbata
11 (1) Corolla campanulate or tubular-campanulate, with well-marked nectar pouches, 5-lobed; stamens 10.   (12)
+ Corolla (5–)6–10-lobed, with or without nectar pouches; stamens (10–)12–18.   (17)
12 (11) Corolla white or yellow to pinkish red.   (13)
+ Corolla deep red.   (14)
13 (12) Leaves elliptic to obovate, abaxial surface with persistent soft or stiff hairs along central veins.   7 Rhododendron subsect. Maculifera
+ Leaves elliptic to lanceolate, abaxial surface glabrous or with simple hairs   10 Rhododendron subsect. Irrorata
14 (12) Corolla fleshy, without spots; ovary densely hairy.   (15)
+ Corolla thin or fleshy, with or without spots; ovary often glabrous.   (16)
15 (14) Small shrubs, rarely creeping; inflorescence often 1–12-flowered.   21 Rhododendron subsect. Neriiflora
+ Small trees; inflorescence dense, often 20–25-flowered.   13 Rhododendron subsect. Arborea
16 (14) Leaf blade orbicular to elliptic, abaxial surface glabrous or hairy; calyx 2–15 mm.   23 Rhododendron subsect. Thomsonia
+ Leaf blade elliptic, abaxial surface densely pilose or lanate; calyx 0.5–1 mm.   22 Rhododendron subsect. Fulgensia
17 (11) Corolla (5–)7–8(–10)-lobed; leaves large, elliptic.   (18)
+ Corolla 5-lobed; leaves small, ovate-elliptic or lanceolate.   (23)
18 (17) Abaxial surface of leaves conspicuously hairy when mature.   (19)
+ Abaxial surface of mature leaves glabrous or with a thin agglutinated indumentum.   (21)
19 (18) Abaxial surface of leaves generally with 2 layers of hairs, outer layer cupular.   4 Rhododendron subsect. Falconera
+ Abaxial surface of leaves with 1 or 2 layers of hairs, hairs never cupular.   (20)
20 (19) Ovary pilose, rarely glandular, or if glabrous then with abaxial surface of leaves viscid-hairy.   3 Rhododendron subsect. Grandia
+ Ovary glabrous, rarely glandular or pilose, abaxial surface of leaves often pannose.   14 Rhododendron subsect. Taliensia
21 (18) Leaves (9–)20–70 cm; ovary densely tomentose, rarely glandular or glabrous.   3 Rhododendron subsect. Grandia
+ Leaves less than 20 cm; ovary glabrous or glandular.   (22)
22 (21) Corolla broadly campanulate, without basal nectar pouches; ovary glabrous or glandular.   1 Rhododendron subsect. Fortunea
+ Corolla campanulate or tubular-campanulate, with basal nectar pouches; ovary glandular, with or without a thin indumentum.   10 Rhododendron subsect. Irrorata
23 (17) Abaxial leaf surface glabrous; peduncle 5–60 mm.   (24)
+ Abaxial leaf surface hairy (rarely glabrous in subsect. Taliensia).   (26)
24 (23) Leaves ovate to orbicular; peduncle 2–5 mm.   6 Rhododendron subsect. Campylocarpa
+ Leaves lanceolate to elliptic; peduncle 5–25(–60) mm.   (25)
25 (24) Peduncles 10–25 mm; corolla campanulate to funnelform.   11 Rhododendron subsect. Pontica
+ Peduncles 5–10 mm; corolla broadly campanulate.   10 Rhododendron subsect. Irrorata
26 (23) Leaf blade ovate to obovate, sometimes narrow; corolla funnelform or campanulate, generally with deeply colored spots.   (27)
+ Leaf blade ovate to obovate or orbicular; corolla campanulate, broadly campanulate, rarely funnelform, with or without deeply colored spots.   (29)
27 (26) Peduncle short; pedicels short; flowers densely arranged; calyx 0.5–1.5 mm.   14 Rhododendron subsect. Taliensia
+ Peduncle long; pedicels slender, long; flowers loosely arranged; calyx 1–3(–5) mm.   (28)
28 (27) Abaxial surface of leaves with silvery white, pale yellow or yellowish-brown hairs; capsule cylindric, straight.   12 Rhododendron subsect. Argyrophylla
+ Abaxial surface of leaves with gray-white to rufous-brown hairs; capsule slender, curved.   15 Rhododendron subsect. Fulva
29 (26) Ovary glabrous; peduncles 10–25 mm; leaves ovate to broadly elliptic.   17 Rhododendron subsect. Campanulata
+ Ovary densely hairy; peduncles 2–20 mm.   (30)
30 (29) Ovary densely pilose to stipitate-glandular; peduncle 10–20 mm.   7 Rhododendron subsect. Maculifera
+ Ovary pilose to thinly glandular; peduncle 3–10 mm.   (31)
31 (30) Abaxial leaf surface with one layer of hairs; ovary densely pilose or tomentose and glandular; young shoots always tomentose; calyx 1–2 mm.   16 Rhododendron subsect. Lanata
+ Abaxial leaf surface with one or two layers of thin to dense hairs; ovary thinly or densely pilose and glandular; if young shoots tomentose then calyx often more than 2 mm.   14 Rhododendron subsect. Taliensia

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