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Rhododendron maximum

(Great Laurel, Rosebay Rhododendron, White Rosebay)

Interesting Facts:

  • Rhodo means "rose" in Latin, dendron means "tree." This particular "rose-tree" has white flowers and pale pink buds. Notice the green dotted nectar guides on the top petals.
  • The toxin found in the leaves of Rhododenron is andromedotoxin, it is poisonous to all domesticated animals.

Conservation Status

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Population Analysis

  • For the 835,580 species in the Class Magnoliopsida (Dicotyledons), we average 4.30 observations each in our database; for the Rosebay Rhododendron, we have 543 observations. Compared to other species in this Class, this species is extremely common.
  • A two-sample t-test can be used to determine whether the trend in observations of the Rosebay Rhododendron is the same as the trend in observations of Magnoliopsida. Is this species just as common, as a proportion of all observations, as it once was? The answer is no, changes in observation rate of this species significantly differ from changes in observation rate of its Class. (t=4.217, p<0.001)
  • How do observation rates of the Rosebay Rhododendron differ from those of Magnoliopsida? To answer this, we examined the percentage of observerations for Magnoliopsida that were observations of the Rosebay Rhododendron each year. We then correlated this percentage with observation year. If observations of the Rosebay Rhododendron are becoming more common relative to other species of Magnoliopsida, the correlation should be positive, but if it is becoming less common, the correlation should be negative. In fact, the correlation is negative (r=-.43), with a negative slope (m = -.000), suggesting that the Rosebay Rhododendron may be in decline relative to other species of Magnoliopsida. This correlation is statistically significant. (F = 67.1, p<.05)
  • The scatter chart to the right shows the percentage of all observations for Magnoliopsida each year that were observations of the Rosebay Rhododendron.

Taxonomy

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Unambiguous Synonyms:

  1. Rhododendron ashleyi Coker

Notes:

Name Status: Accepted Name. Latest taxonomic scrutiny: 15-Mar-2000.

Place of publication: Sp. pl. 1:392. 1753

Name verified on 06-Jun-1995 by ARS Systematic Botanists. Last updated: 12-Sep-2003

Physical Description

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Genus Rhododendron:

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.[1]

ID Features: Long evergreen, strap-like leaves. Large flower buds surround by leaf-like bracts at the base. Large size for a rhododendron. Late blooming rhododendron (late June). •

Habit: A multi-stemmed, large, evergreen shrub. Branching habit is upright and spreading to irregular.

Flowers: Blooms later than most large-leaved rhododendrons in late June. Flowers are rose-pink, pink margined, or nearly white. Newly emerging shoot sometimes partially obscure the flowers. Individual flowers are 1.5" across and are borne in crowned clusters of up. to 25 flowers. Flower buds are distictly larger than vegetative buds.. Flower bud are surrounded at the base with leaf-like bracts. • Bloom Period: April, May, June. • Flower Color: near white, pink, white

Seeds: Fruit: Dehiscent capsule. Not ornamentally attractive.

Foliage: Summer foliage: Leaves are evergreen, broadest above the middle. Leaves are thick, leathery and dark green. 4" to 8" long, somewhat strap-like. Underside of leaves is either green or a light rusty color. Upperside is dark green. • Fall foliage: No fall color. Evergreen.

Images:

Distribution

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Range and Population

Eastern North America.

Native: Alabama, Connecticut, Georgia, Kentucky, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Nova Scotia, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia.

Landscaping

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Landscape Uses: Shrub border. Shady locations. Naturalistic areas. Edge of woods. As a screen. • Liabilities: Lacebug. Phytophthora root rot. Winterburn in exposed sites. Chlorosis on high pH soils. Leaves roll up in temperatures below 25o F to conserve moisture. and unfurl when warm temperatures return. Flowers partially hidden by new shoots. • Care: Apply Holly-tone in early spring and after flowering. Amend poorly-drained soils with fine-grade mulch.

Habitat

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Zone 4.

Reproduction

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Duration: Perennial

Growth

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Culture: Partial shade; tolerates relatively dense shade. Moist, cool, acidic, well-drained, organic soil. Avoid windswept, exposed or hot locations. Remove flower clusters following bloom to stimulate new growth and flower. bud set. Transplant from containers or B&B..

Soil: Soil: Needs acidic, well-drained, organic soil. • Minimum pH: 4.5 • Maximum pH: 6.5

Sunlight: Sun Exposure: Light Shade.

Temperature: Cold Hardiness: 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b. (map)

Similar Species

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Rosebay rhododendron flowers are white, and Catawba flowers are pink.

Members of the genus Rhododendron:

There are approximately 8,358 species, subspecies, varieties, forms, and cultivars in this genus. Here are just 100 of them: R. borneense angustissimum · R. brookeanum gracile · R. dalhousiae tashii · R. edanoi pneumonanthum · R. floccigerum appropinquans · R. henanense lingbaoense · R. javanicum brookeanum · R. javanicum gracile · R. javanicum schadenbergii · R. mariae kwangsiense · R. orbiculare oblongum · R. przewalskii chrysophyllum · R. przewalskii huzhuense · R. ririei leiboense · R. scabrum amanoi · R. simiarum youngae · R. tomentosum subarcticum · R. trichocladum nepalense · R. yakusimanum makinoi · R. yunnanensis bhutanica · R. '851C' · R. 'A. Gilbert' · R. 'A.J. Ivens' · R. 'Abbot' · R. 'Abe Arnott' · R. 'Abegail' · R. 'Abendrot' · R. 'Accent' · R. 'Accomplishment' · R. 'Achilles' · R. 'Actress' · R. 'Ada Brunieres' · R. 'Adamant' · R. 'Addy Wery' · R. 'Adelaide' · R. 'Admiral Piet Hein' · R. 'Adonis' · R. 'Adorable' · R. 'Adriaan Koster' · R. 'Adriaan Koster' × wardii var. wardii Litiense Group · R. 'Advance' · R. 'Aeolus' · R. 'Agamujin' · R. 'Ageeth' · R. 'Agemaki' · R. 'Agnes Beaufort' · R. 'Agnes Lamont' · R. 'Agnes Lamont' × lacteum · R. 'Agnes Mangles' · R. 'Agnes' · R. 'Ahren's Favourite' · R. 'Aida' (Aida Rustica Flora Pleno Hybrid Azalea) · R. 'Aileen O'Rourke' · R. 'Ailsa Jean' · R. 'Aioi' · R. 'Airy Fairy' · R. 'Aizen-no-tsuki' · R. 'Akebono-ryukyu' · R. 'Aksel Olsen' · R. 'Aladdin' (Aladdin Azalea) · R. 'Aladdin's Jinni' · R. 'Alan Campbell-Johnson' · R. 'Alan Stockman' · R. 'Albacore' · R. 'Albarello' · R. 'Albatross Townhill Pink' · R. 'Albatross Townhill White' · R. 'Albatross' · R. 'Albert Schweitzer' · R. 'Album Elegans' (Album Elegans Rhododendron) · R. 'Album' · R. 'Alcesta' · R. 'Alena' · R. 'Alessandro Volta' · R. 'Alex Hill' · R. 'Alexander' · R. 'Alexandra Gordon' · R. 'Alfred' · R. 'Alice de Stuers' · R. 'Alice Gilbert' · R. 'Alice Hennessy' · R. 'Alice Mangles' · R. 'Alice Martineau' · R. 'Alice Street' · R. 'Alice' · R. 'Alight' (Alight Azalea) · R. 'Alisa Nicole' (Vireya Rhododendron) · R. 'Alison Johnstone' · R. 'Alix' · R. 'All-a-Glow' · R. 'Allegory' (Allegory Azalea) · R. 'Allen's Surprise' · R. 'Allure' (Allure Glenn Dale Azalea) · R. 'Aloha' (Deciduous Azalea) · R. 'Alpine Dew' · R. 'Alpine Gem' · R. 'Alpine Glow' · R. 'Altaclerense' · R. 'Always a Lady' · R. 'Alyssa Nori'

Bibliography

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  • Chamberlain, D. F. 1982. A revision of Rhododendron II. Subgenus Hymenanthes. Notes Roy. Bot. Gard. Edinburgh 39:316.
  • Gleason, H. A. & A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada, ed. 2. (Glea Cron ed2)
  • Huxley, A., ed. 1992. The new Royal Horticultural Society dictionary of gardening. (Dict Gard)
  • Kartesz, J. T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. (L US Can ed2)
  • Krüssmann, G. 1984. Handbuch de Laubgeholze, Engl. translat. (Krussmann) ["little garden merit"].
  • Luteyn, J. L. et al. 1996. Ericaceae of the southeastern United States. Castanea 61:119.
  • Scoggan, H. J. 1978–1979. The flora of Canada, 4 vol. (F Canada)
  • Seymour, F. 1969. The flora of New England. (F NEng)
  • Terrell, E. E. et al. 1986. Agric. Handb. no. 505. (AH 505)
  • Walters, S. M. et al., eds. 1986–. European garden flora. (Eur Gard F)

More Info

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Notes

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Contributors:

  • Bisby, F.A., Y.R. Roskov, M.A. Ruggiero, T.M. Orrell, L.E. Paglinawan, P.W. Brewer, N. Bailly, J. van Hertum, eds (2007). Species 2000 and ITIS Catalogue of Life: 2007 Annual Checklist. Species 2000: Reading, U.K.
  • Global Biodiversity Information Facility. Accessed November 28, 2007. http://www.gbif.org Mediated distribution data from 22 providers.
  • Light, Kris. East Tennessee Wildflowers
  • USDA, ARS, National Genetic Resources Program. Germplasm Resources Information Network - (GRIN) [Online Database]. National Germplasm Resources Laboratory, Beltsville, Maryland. URL (April 30, 2008)

Data Sources:

Accessed through GBIF Data Portal November 28, 2007:

Identifiers:

Footnotes:

  1. Fang Mingyuan, Fang Ruizheng, He Mingyou, Hu Linzhen, Yang Hanbi, David F. Chamberlain "Rhododendron". in Flora of China Vol. 14 Page 260. Published by Science Press (Beijing) and Missouri Botanical Garden Press. Online at EFloras.org.

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Last Revised: May 11, 2008