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12. Rhododendron Linnaeus, Sp. Pl. 1: 392. 1753.
杜鹃属 du juan shu
Fang Mingyuan (方明渊), Fang Ruizheng (方瑞征 Fang Rhui-cheng), He Mingyou (何明友), Hu Linzhen (胡琳贞 Hu Ling-cheng), Yang Hanbi (杨汉碧 Yang Han-pi); David F. Chamberlain
Shrubs or trees, terrestrial or epiphytic, with various hairs, and/or with peltate scales or glabrous, indumentum sometimes detersile (the hairs tangled and coming away as a layer). Leaves evergreen, deciduous or semideciduous, alternate, sometimes clustered at stem apex; margin entire, very rarely crenulate, abaxial indumentum sometimes with a pellicle (a thin skinlike layer on the surface). Inflorescence a raceme or corymb, mostly terminal, sometimes lateral, few- to many-flowered, sometimes reduced to a single flower. Calyx persistent, 5–8-lobed, sometimes reduced to a rim, lobes minute and triangular to large and conspicuous. Corolla funnelform, campanulate, tubular, rotate or hypocrateriform, regular or slightly zygomorphic, 5(–8)-lobed, lobes imbricate in bud. Stamens 5–10(–27), inserted at base of corolla, usually declinate; filaments linear to filiform, glabrous or pilose towards base; anthers without appendages, opening by terminal or oblique pores. Disk usually thick, 5–10(–14)-lobed. Ovary 5(–18)-locular, with hairs and/or scales, rarely glabrous. Style straight or declinate to deflexed, persistent; stigma capitate-discoid, crenate to lobed. Capsule cylindrical, coniform, or ovoid, sometimes curved, dehiscent from top, septicidal; valves thick or thin, straight or twisted. Seeds very numerous, minute, fusiform, always winged, or both ends with appendages or thread-like tails.
About 1000 species: Asia, Europe, North America, two species in Australia; 571 species (409 endemic) in China.
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| 1 |
Inflorescence buds lateral, usually in axils of upper or lower leaves of last year’s shoots; uppermost inflorescence buds (or leaf bud) in axils of uppermost leaves, subterminal. |
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(2) |
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Inflorescence buds terminal, sometimes with additional lateral floral buds immediately below, vary rarely axillary from lower leaves (as in some species of R. subsect. Cinnabarina). |
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(4) |
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| 2 (1) |
New foliage shoots from axils of leaves below inflorescence buds; leaves with peltate scales,
deciduous or semievergreen; flowers appearing before leaf emergence. |
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4 Rhododendron subg. Rhodorastrum |
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New foliage shoots arising from uppermost (pseudoterminal) buds, and from axils of leaves; leaves evergreen. |
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(3) |
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| 3 (2) |
Plants with peltate scales; capsule short, cylindric. |
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3 Rhododendron subg. Pseudorhodorastrum |
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Plants without peltate scales; capsule conical-ovoid or cylindric. |
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6 Rhododendron subg. Azaleastrum |
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| 4 (1) |
Plant with peltate scales, sometimes also with other hairs. |
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(5) |
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Plant without peltate scales, with various hairs, or glabrous. |
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(6) |
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| 5 (4) |
Leaves evergreen, very rarely semideciduous to deciduous; flowers appearing after leaf emergence; style usually straight; plant usually without hairs. |
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1 Rhododendron subg. Rhododendron |
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Leaves deciduous or semideciduous, very rarely evergreen; flowers appearing before leaf emergence; style usually short and recurved; plant usually hairy. |
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2 Rhododendron subg. Pseudazalea |
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| 6 (4) |
Corolla divided nearly to base on lower side; peduncle bearing leafy bracts; style curved. |
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9 Rhododendron subg. Therorhodion |
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Corolla not divided to base; peduncle without bracts; style slender, straight. |
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(7) |
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| 7 (6) |
Flowers and new leafy shoots from same terminal buds; leaves persistent to deciduous; indumentum often with strap-shaped setae. |
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8 Rhododendron subg. Tsutsusi |
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Flowers from terminal buds; new leafy shoots from lateral buds, i.e., from axils of leaves of previous season; indumentum without flattened setae. |
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(8) |
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| 8 (7) |
Leaves evergreen; stamens 10(–20) |
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5 Rhododendron subg. Hymenanthes |
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Leaves deciduous; stamens 5 (in Chinese species). |
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7 Rhododendron subg. Pentanthera |
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List of lower taxa
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