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Rhododendron

Rhododendron
Family: Ericaceae
Rhododendron image
Paul Rothrock
  • FNA
  • Gleason & Cronquist
  • Gleason & Cronquist
  • Resources
Walter S. Judd, Kathleen A. Kron in Flora of North America (vol. 8)
Subshrubs, shrubs, or trees, (rhizomatous or not). Stems erect (and/or creeping, prostrate in R. groenlandicum, R. lapponicum, R. tomentosum); twigs hairy or glabrous, (older twigs without peglike projections). Leaves persistent or deciduous, alternate; petiole present; blade coriaceous to membranous, (base cuneate, rounded, or obtuse), margins entire, (sometimes ciliate, plane to revolute, abaxial surface 1/3+ visible except sometimes in bud, surfaces hairy and/or scaled, midvein hairy or not, adaxial surface sometimes impressed; venation usually brochidodromous). ( Winter buds usually large, with imbricate scales; floral buds usually larger than vegetative buds.) Inflorescences terminal (axillary in R. albiflorum, short, corymbiform or rounded racemes (fasciculate racemes in R. canadense, R. lapponicum; fasciculate in R. albiflorum), 3-35-flowered (1-2-flowered in R. albiflorum); perulae brownish, scalelike, dry. ( Pedicels horizontal to erect (recurved); bracteoles 2, brownish, scalelike, basal.) Flowers bisexual, weakly bilaterally symmetric (radially symmetric in R. columbianum, R. groenlandicum, R. tomentosum, scented or not); sepals 5[-9], slightly connate; petals 5[-9], strongly to only slightly connate (sometimes nearly distinct), corolla deciduous, rotate to campanulate or funnelform; stamens 5-12[-20], included to long-exserted; (filaments usually unequal, usually unicellular-hairy, glabrous in R. vaseyi, glabrous or proximally unicellular-hairy in R. groenlandicum, R. lapponicum); anthers without awns, dehiscent by terminal pores; ovary 5[-18]-locular; style inserted in slight depression at ovary apex or smoothly intergrading, (usually curved, long, slender); stigma capitate. Fruits capsular, elongate, usually ovoid to cylindric, dehiscence usually basipetally septicidal (acropetally septicidal in R. columbianum, R. groenlandicum, R. tomentosum). Seeds (10-)100+, flattened-ellipsoidal to fusiform, often tailed, ± winged; testa smooth. x = 13.

R. Good (1974) provided an excellent discussion of the phytogeography of Rhododendron, which occurs in arctic to tropical montane regions of North America, Europe, and Asia, extending southward to northeastern Australia. Its main centers of diversity are in the mountains of southern China and bordering countries, with a secondary center in New Guinea; eastern North America is a third center of diversity.

The species of Rhododendron are divided into subgenera (see references and discussion under various representative species). The subgenera are occasionally segregated; see, for example, H. F. Copeland (1943). The name Azalea Linnaeus often has been used for species with deciduous leaves; such use is misapplied.

Therorhodion has usually been included within Rhododendron, and these species are then placed in subg. Therorhodion (Maximowicz) A. Gray (W. R. Philipson and M. N. Philipson 1986). Here, Therorhodion is recognized as a genus distinct from Rhododendron (see K. A. Kron and W. S. Judd 1990; Kron 1997; Kron et al. 2002) because of its foliaceous perulae and base chromosome number of 12. Therorhodion probably is sister to the remaining genera of Rhodoreae (most of which belong within Rhododendron). Rhododendron is closely related to Menziesia, and the recognition of the latter may render Rhododendron paraphyletic (Kron 1997).

Numerous non-native species are grown for their beautiful flowers, and some of these, e.g., Rhododendron molle (Blume) G. Don, R. luteum Sweet, R. simsii Planchon, and R. obtusum (Lindley) Planchon, sometimes persist after cultivation. Probably, all species are poisonous due to the presence of andromedotoxin, a resinoid (M. D. McGee 1973).

Vascular plants of NE US and adjacent Canada
Cal 5-lobed, much shorter than the cor; cor campanulate to funnelform, conspicuous, regularly or commonly irregularly 5-lobed; stamens mostly 5 or 10, with elongate filaments and short anthers with 2 terminal pores; ovary superior, 5-locular; style elongate; capsule septicidal; shrubs or trees with alternate, deciduous or evergreen lvs and showy fls in terminal racemes or umbel-like clusters from scaly buds. Our spp. 2n=26, except as noted. (Azalea) 850, mainly N. Hemisphere.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.
Vascular plants of NE US and adjacent Canada
Fls 5-merous; cal-lobes very short; pet 5, separate, spreading; stamens 5-10; filaments slender; anthers short, dorsifixed, with 2 terminal pores; ovary puberulent, 5- locular; style elongate; capsule septicidal; erect or diffuse, freely branched shrubs with thick, evergreen, alternate, sessile or subsessile lvs and long-pedicellate fls in a crowded (sometimes umbelliform) terminal corymb. 5, boreal.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.
<< 51 - 100 taxa >>
Rhododendron ciliatum
Media resource of Rhododendron ciliatum
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Rhododendron ciliicalyx
Media resource of Rhododendron ciliicalyx
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Rhododendron cinnabarinum
Media resource of Rhododendron cinnabarinum
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Rhododendron citriniflorum
Media resource of Rhododendron citriniflorum
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Rhododendron colemanii
Media resource of Rhododendron colemanii
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Rhododendron collettianum
Media resource of Rhododendron collettianum
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Rhododendron columbianum
Media resource of Rhododendron columbianum
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Rhododendron concinnum
Media resource of Rhododendron concinnum
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Rhododendron crinigerum
Media resource of Rhododendron crinigerum
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Rhododendron cumberlandense
Media resource of Rhododendron cumberlandense
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Rhododendron dasycladoides
Media resource of Rhododendron dasycladoides
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Rhododendron dauricum
Media resource of Rhododendron dauricum
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Rhododendron davidsonianum
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Rhododendron decorum
Media resource of Rhododendron decorum
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Rhododendron degronianum
Media resource of Rhododendron degronianum
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Rhododendron delavayi
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Rhododendron dendricola
Media resource of Rhododendron dendricola
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Rhododendron dichroanthum
Media resource of Rhododendron dichroanthum
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Rhododendron dielsianum
Media resource of Rhododendron dielsianum
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Rhododendron dilatatum
Media resource of Rhododendron dilatatum
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Rhododendron discolor
Media resource of Rhododendron discolor
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Rhododendron diversipilosum
Media resource of Rhododendron diversipilosum
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Rhododendron eastmanii
Media resource of Rhododendron eastmanii
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Rhododendron edgeworthii
Media resource of Rhododendron edgeworthii
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Rhododendron ericoides
Media resource of Rhododendron ericoides
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Rhododendron eriocarpum
Media resource of Rhododendron eriocarpum
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Rhododendron faberi
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Rhododendron fallacinum
Media resource of Rhododendron fallacinum
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Rhododendron fastigiatum
Media resource of Rhododendron fastigiatum
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Rhododendron ferrugineum
Media resource of Rhododendron ferrugineum
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Rhododendron flammeum
Media resource of Rhododendron flammeum
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Rhododendron flavidum
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Rhododendron floccigerum
Media resource of Rhododendron floccigerum
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Rhododendron formosanum
Media resource of Rhododendron formosanum
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Rhododendron formosum
Media resource of Rhododendron formosum
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Rhododendron forrestii
Media resource of Rhododendron forrestii
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Rhododendron fortunei
Media resource of Rhododendron fortunei
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Rhododendron fulgens
Media resource of Rhododendron fulgens
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Rhododendron gandavense
Media resource of Rhododendron gandavense
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Rhododendron genestierianum
Media resource of Rhododendron genestierianum
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Rhododendron glaucum
Media resource of Rhododendron glaucum
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Rhododendron goyozanense
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Rhododendron gracilentum
Media resource of Rhododendron gracilentum
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Rhododendron groenlandicum
Media resource of Rhododendron groenlandicum
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Rhododendron haematodes
Media resource of Rhododendron haematodes
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Rhododendron hainanense
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Rhododendron hanceanum
Media resource of Rhododendron hanceanum
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Rhododendron herzogii
Media resource of Rhododendron herzogii
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Rhododendron himantodes
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Rhododendron hippophaeoides
Media resource of Rhododendron hippophaeoides
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