12. RHODODENDRON Linnaeus, Sp. Pl. 1: 392. 1753
Total Page:16
File Type:pdf, Size:1020Kb
Flora of China 14: 260–455. 2005. 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. 1a. 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. 2a. New foliage shoots from axils of leaves below inflorescence buds; leaves with peltate scales, deciduous or semievergreen; flowers appearing before leaf emergence ............................................. 4. R. subg. Rhodorastrum 2b. New foliage shoots arising from uppermost (pseudoterminal) buds, and from axils of leaves; leaves evergreen. 3a. Plants with peltate scales; capsule short, cylindric ............................................................. 3. R. subg. Pseudorhodorastrum 3b. Plants without peltate scales; capsule conical-ovoid or cylindric .................................................... 6. R. subg. Azaleastrum 1b. 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). 4a. Plant with peltate scales, sometimes also with other hairs. 5a. Leaves evergreen, very rarely semideciduous to deciduous; flowers appearing after leaf emergence; style usually straight; plant usually without hairs ..................................................... 1. R. subg. Rhododendron 5b. Leaves deciduous or semideciduous, very rarely evergreen; flowers appearing before leaf emergence; style usually short and recurved; plant usually hairy .................................................... 2. R. subg. Pseudazalea 4b. Plant without peltate scales, with various hairs, or glabrous. 6a. Corolla divided nearly to base on lower side; peduncle bearing leafy bracts; style curved .......... 9. R. subg. Therorhodion 6b. Corolla not divided to base; peduncle without bracts; style slender, straight. 7a. Flowers and new leafy shoots from same terminal buds; leaves persistent to deciduous; indumentum often with strap-shaped setae ....................................................................................... 8. R. subg. Tsutsusi 7b. Flowers from terminal buds; new leafy shoots from lateral buds, i.e., from axils of leaves of previous season; indumentum without flattened setae. 8a. Leaves evergreen; stamens 10(–20) .................................................................................. 5. R. subg. Hymenanthes 8b. Leaves deciduous; stamens 5 (in Chinese species) ............................................................. 7. R. subg. Pentanthera 1. Rhododendron subg. Rhododendron 杜鹃亚属 du juan ya shu Shrubs, more rarely trees, usually evergreen, seldom deciduous, sometimes epiphytic; young shoots densely scaly, often without hairs, sometimes also pubescent, hispid or woolly. Leaf blade normally leathery; abaxial surface densely scaly, often also adaxial leaf surfaces, pedicels, calyx, corolla, ovary, and style, hairs generally absent, rarely simple pilose. Inflorescence terminal or axillary, um- bellate-racemose or shortly racemose, 1- to many-flowered: flowers opening after leaf emergence. Calyx usually small or not well- developed, 5-lobed; corolla small to large, funnelform to campanulate, tubular-campanulate or salver-shaped, only rarely actinomor- phic, white, red, yellow or purple, flecked within; stamens (5–)10(–27). Ovary 5–6(–12)-locular; style declinate to deflexed. Capsule oblong or ovoid, densely scaly, valves subwoody, deflexed on splitting. Seeds many, sometimes with appendages at both ends. About 500 species: Asia, Europe, North America, two species in Australia; 184 species (113 endemic) in China. 1a. Capsules with rather thin valves that twist after dehiscence; placenta generally free from central axis of capsule; seeds with tail-like appendages at both ends ............................................................................................................ 3. R. sect. Vireya 1b. Capsules with hard or woody valves; placenta remaining joined to central axis of capsule; seeds with finned wings. Flora of China 14: 260–455. 2005. 2a. Stamens (5–)10(–27), usually exserted from corolla tube; corolla often large, funnelform, campanulate or tubular; scales with margin entire, rarely crenulate ......................................................................... 1. R. sect. Rhododendron 2b. Stamens 5–8, rarely 10, included within corolla tube; corolla often small, salver-shaped; scales with margin lacerate ........................................................................................................................................ 2. R. sect. Pogonanthum 1. Rhododendron sect. Rhododendron 杜鹃组 du juan zu Shrubs, sometimes prostrate or cushion-forming, or small trees, usually evergreen, seldom deciduous, sometimes epiphytic. Leaves small to large; leaf blade margin usually entire, sometimes crenulate or revolute; abaxial surface scaly, sometimes also uni- formly woolly, or pubescent or strap-shaped-setose along main veins. Inflorescence terminal, 1–28-flowered, or 2- or 3-flowered and axillary, usually umbellate-racemose, shortly racemose or capitate; flowers small to large. Calyx generally short, lobes leaflike or ab- sent, rarely well-developed; corolla funnelform, to campanulate or tubular-campanulate. Stamens (4–)5–10(–25); filaments mostly pubescent towards base, rarely glabrous; ovary 5(–12)-locular, always scaly, sometimes also hairy; style long, slender, straight, curved, or sharply deflexed, glabrous or with scales or shortly pilose at base. Capsule ovoid to cylindric, valves woody, 2–23(–70) mm, scaly or not, sometimes pubescent. Seeds wingless or with a finlike wing. About 170 species: mostly in Asia, especially from the E Himalayas to SW China, a few species in Europe and North America; 153 species (92 endemic) in China. 1a. Style short, thick, distinctly curved. 2a. Stamens 12–16; corolla with woolly hairs in the throat .................................................................. 15. R. subsect. Camelliiflora 2b. Stamens (8–)10; corolla glabrous inside. 3a. Scales strongly dimorphic, the larger dark brown, the smaller golden .............................................. 16. R. subsect. Glauca 3b. Scales on abaxial leaf surface monomorphic. 4a. Pedicels shorter than corolla; corolla usually yellow, rarely white or pink ............................... 14. R. subsect. Boothia 4b. Pedicels distinctly longer than corolla. 5a. Inflorescences corymbose, 1–3(–5)-flowered; leaves 0.4–2.6(–4) cm. 6a. Corolla fleshy, crimson or purple, with scales outside; abaxial leaf surface with distant scales ......................................................................................................... 17. R. subsect. Campylogyna 6b. Corolla thinner, variable in color, with dense scales outside; abaxial leaf surface with dense scales ........................................................................................................... 19. R. subsect. Lepidota 5b. Inflorescences racemose, 4–10(–18)-flowered; leaves (2–)4–5 cm. 7a. Scales entire, small, distant on abaxial surface of leaves; corolla campanulate ............................................................................................................................... 18. R. subsect. Genestieriana 7b. Scales crenulate, overlapping on abaxial surface of leaves; corolla rotate .................... 20. R. subsect. Baileya 1b. Style slender and straight. 8a. Leaf blade abaxially woolly, hairs obscuring small golden scales .................................................... 1. R. subsect. Edgeworthia 8b. Leaf blade abaxially without hairs, or rarely with hairs that do not obscure the scales. 9a. Style with scales, at least at base, sometimes up to tip, rarely without scales; calyx usually conspicuously lobed, occasionally with underdeveloped lobes, then with margin