Skip to main content
×
×
Home

A revision of Rhododendron section Pentanthera

  • K. A. Kron (a1)
Abstract

Rhododendron sect. Pentanthera G. Don (Ericaceae) comprises a group of closely related, highly ornamental plants which are commonly called ‘azaleas'. Thirteen of the fifteen species recognized in this section are indigenous to North America. One species (R. molle) is native to Japan and China, and one species (R. luteum) is indigenous to the Caucasus region. Phylogenetic analysis of the species within the section indicates that R. molle is the sister to the rest of the section. It is the sole member of R. subsect. Sinensia. The remaining species form a monophyletic group recognized as R. subsect. Pentanthera. Within this subsection the presence of a blotch on the upper corolla lobe defines two primarily orange to red-flowered groups. The first group has a Tertiary Period disjunct distribution and comprises R. luteum, R. austrinum and R. occidentale. The second group is indigenous to eastern North America and comprises R. calendulaceum, R. cumberlandense, R. flammeum, R. prunifolium and R. alabamense. In both groups the cladistically basal species has white flowers with a yellow blotch on the upper corolla lobe (R. occidentale, R. alabamense, respectively). The pink to white early flowering species R. canescens, R. periclymenoides and R. prinophyllum do not form a monophyletic group.

Phenetic analyses indicate that the eastern Asian taxon, R. molle, is best recognized as one species with two geographical subspecies; Rhododendron prinophyllum is quite distinct from R. canescens and R. periclymenoides. The latter two species are very similar morphologically, but their similarities are due to the retention of primitive characters and they should be recognized as distinct species. Rhododendron calendulaceum can be distinguished from R. cumberlandense using a combination of morphological and phenological characters. The various taxa previously segregated out of R. viscosum are merely extreme forms of a widespread and variable species and are not given any formal rank. No subspecific taxa are recognized for R. occidentale. Distribution maps, keys to the species, species descriptions and specimen citations are included.

Copyright
References
Hide All
Alexander, E. G. (1935). Azalea arborescens. Addisonia 19: 1718, pl. 617.
André, E. F. (1871). Azalea mollis Blume. Mini Hort. 18: 132 t. 68.
Ashe, W. W. (1921). Notes on Rhododendron. Rhodora 23: 177179.
Barnhart, J. H. (1895). Proceedings of the Torrey Botanical Club, Wed. evening. Bull. Torrey Bot. Club 22: 282.
Bartram, W. (1791). Travels in North and South Carolina, Georgia and East Florida. Ed. 1. James and Johnson, Philadelphia.
Blanchard, W. H. (1902). Some Vermont and New Hampshire plants in the Middle Connecticut Valley. I. Rhodora 4: 129133.
Bowers, C. G. (1927). Rhododendrons and azaleas for breeding purposes in America. J. New York Bot. Gard. 28: 8186.
Bowers, C. G. (1936). Rhododendrons and azaleas. Their origins, cultivation and development. Macmillan, New York.
Bowers, C. G. (1954). Winter hardy azaleas and rhododendrons. The Massachusetts Hort. Soc., Boston.
Braun, E. L. (1941). The red azaleas of the Cumberlands. Rhodora 43: 3135.
Clausen, R. T. (1941). On the uses of the terms “subspecies” and “variety”. Rhodora 43: 157167.
Coker, J. L. (1920). Azalea atlantica Ashe and its variety luteo-alba n. var. J. Elisha Mitchell Sci. Soc. 36: 9799.
Cowan, J. M. (1950). The rhododendron leaf: a study of epidermal appendages. Oliver & Boyd, Edinburgh.
Creech, J. L. (1962). A distribution note on Rhododendron japonicum. Amer. Hort. Mag. 41: 174177.
Cullen, J. (1980). Rhododendron taxonomy and nomenclature. In: Luteyn, J. ' Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf, pp. 2738. NY Bot. Garden, Bronx, NY.
Day, M. A. (1899). Plants from the eastern slope of Mt. Equinox. Rhodora 1: 220222.
Dequeiroz, K. & Donoghue, M. J. (1988). Phylogenetic systematics and the species problem. Cladistics 4: 7781.
Dequeiroz, K. & Donoghue, M. J. (1990). Phylogenetic systematics and species revisited. Cladistics 6: 8390.
Donoghue, M. J. (1985). A critique of the biological species concept and recommendations for a phylogenetic alternative. Bryologist 88: 172181.
Donoghue, M. J. & Cantino, P. D. (1984). The logic and limitations of the outgroup substitution approach to cladistic analysis. Syst. Bot. 9: 192202.
Drude, O. (1889). Ericaceae. In: Engler, A. & Prantl, K. (eds) Die natürlichen Pflanzenfamilien, Vol. 4, Part 1, pp. 1565. Hans Melchior and Erich Weidermann, Leipzig.
Duhamel, Du Monceau H. L. (1812). Traite des arbres et arbuste que Von cultivi en France en pleine terre. Vol. 5: 221227.
Evans, D., Kane, K. H., Knights, B. A. & Math, V. B. (1980). Chemical taxonomy of the genus Rhododendron. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf., pp. 187245. NY Bot. Garden, Bronx, NY.
Federal Register. (1980). Endangered and threatened wildlife and plants: Review of plant taxafor listing as endangered or threatened species. Federal Register Vol. 45, No. 242, part iv, lc. 82480–82569. US Department of the Interior, Washington, DC.
Fernald, M. L. (1940). Some spermatophytes of eastern North America. Rhodora 42: 239246.
Fernald, M. L. (1941). Another century of additions to the flora of Virginia. Rhodora 43: 485553.
Fernald, M. L. (1942). Misinterpretation of Atlantic Coastal Plain species. Rhodora 44: 238246.
Galle, F. (1968). Native and some introduced azaleas for southern gardens. Booklet #2. Callaway Gardens, Pine Mt. Georgia.
Galle, F. (1985). Azaleas. Timber Press, Portland, Oregon.
Godfrey, R. K. & Wooten, J. W. (1981). Aquatic and wetland plants of southeastern U.S.: dicotyledons. University of Georgia Press, Athens.
Goldy, R. G. & Lyrene, P. M. (1984). Pentaploid blueberries from 6x x 2x crosses. J. Amer. Soc. Hort. Sci. 109: 218221.
Haberer, J. V. (1905). Plants of Oneida Co., New York and vicinity. I. Rhodora 7: 106110.
Hallé, F., Oldeman, R. A. A. & Tomlinson, P. B. (1978). Tropical trees and forests: an architectural analysis. Springer-Verlag, Berlin.
Harborne, J. B. (1980). Flavonoid pigments as both taxonomic and phyletic markers in the genus Rhododendron. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf, pp. 145161. NY Bot. Garden, Bronx, NY.
Harborne, J. B. & Williams, C. A. (1971). Leaf survey of flavonoids and simple phenols in the genus Rhododendron. Phytochemistry 10: 27272744.
Harkness, B. (1932). Rhododendron atlanticum Rehder. Nat. Hort. Mag. 11: 55.
Hayes, S. F., Keenan, J. & Cowan, J. M. (1951). A survey of the anatomy of the Rhododendron leaf in relation to the taxonomy of the genus. Notes Roy. Bot. Gard. Edinburgh 21: 134.
Hedegaard, J. (1980). Morphological studies in the genus Rhododendron dealing with seeds, fruits and seedlings and their associated hairs. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf., pp. 117144. NY Bot. Garden, Bronx, NY.
Heiser, C. B., Jr (1973). Introgression re-examined. Bot. Rev. 39: 347366.
Hendy, M. D. & Penny, D. (1982). Branch and bound algorithms to determine minimal evolutionary trees. Math. Biosci. 59: 277290.
Hennig, W. (1966). Phylogenetic systematics. University of Illinois Press, Urbana.
Holmgren, P. K., Keuken, W. & Schofield, E. K. (eds) (1981). Index Herbariorum. Part I: The herbaria of the world.Ed.7. Dr W. Junk, B.V. Publ., Boston.
Hsü, J. (1983). Late Cretaceous and Cenozoic vegetation in China, emphasizing their connections with North America. Ann. Missouri Bot. Gard. 70: 490508.
International Code Of Botanical Nomenclature. (1981). E. G. Voss (Chairman). Utrecht, The Netherlands.
Janaki-Ammal, E. K., Enoch, I. C. & Bridgwater, M. (1950). Chromosome numbers in species of Rhododendron. The Rhododendron Yearbook 5: 7891. Royal Horticultural Society.
Jepson, W. L. (1939). A Flora of California 3: 17128.
Judd, W. S. (1981). A monograph of Lyonia (Ericaceae). J. Arnold Arb. 62: 63209, 315–436.
Kellner, C. V. (1978). Are pollinators exerting selection pressure on the azalea hybrids on Gregory Bald? MS thesis. University of Tennessee, Knoxville.
King, B. L. (1977a). The flavonoids of the deciduous Rhododendron of North America. Amer. J. Bot. 64: 350360.
King, B. L. (1977b). Flavonoid analysis of hybridization in Rhododendron section Pentanthera (Ericaceae). Syst. Bot. 2: 1427.
King, B. L. (1980). The systematic implications of flavonoids in Rhododendron subgenus Pentanthera. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf, pp. 163186. NY Bot. Garden, Bronx, NY.
Kingdon-Ward, F. (1935). Rhododendron seeds, with special reference to their classification. J. Bot. 73: 241247.
Knowlton, C. H. (1919). An excursion to Mt. Washington, Mass, and Bash-Bish Falls. Rhodora 21: 198202.
Knowlton, C. H. & Deane, W. (1922). Reports on the flora of the Boston district. XXXVI. Rhodora 24: 152156.
Kron, K. A. (1989). Azalea rosea is a superfluous name. Sida 13: 331333.
Kron, K. A., Gawen, L. M. & Chase, M. W. (1993). Evidence for introgression in azaleas (Rhododendron, Ericaceae): chloroplast DNA and morphological variation in a hybrid swarm on Stone Mountain, Georgia. Amer. J. Bot. 80: 10951099.
Lawrence, G. H. M. (1954). The status of Rhododendron nudiflorum and R. roseum. Baileya 2: 13.
Lemmon, W. P. (1938). Notes on a study of the southeastern azaleas with descriptions of two new species. Bartonia 19: 1417.
Li, H. L. (1952). Floristic relationships between eastern Asia and eastern North America. Trans. Amer. Philos. Soc. 42: 371–29.
Li, H. L. (1957). Chromosome studies in the azaleas of eastern North America. Amer. J. Bot. 44: 814.
Linnaeus, C. (1753). Species Plantarum. 2nd facsimile ed. Ray Society, London.
Little, E. L. (1970). Endemic, disjunct and northern trees in the southern Appalachians. In: Holt, P. C. (ed.) The distributional history of the biota of the southern Appalachians. Part II: Flora. Research Division Monograph 2, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
Luteyn, J. L. (1983). Ericaceae—Part 1. Cavendishia. Fl. Neotrop. Monogr. 35.
Maddison, W. P., Donoghue, M. J. & Maddison, D. R. (1984). Outgroup analysis and parsimony. Syst. Zool. 33: 83103.
Makino, T. (1956). An illustrated flora of Japan. Hokuryukan, Tokyo.
Mayr, E. (1969). Principles of systematic zoology. McGraw-Hill, New York.
McCullough, M. A. (1985). Exploring for the western azalea in southern California. J. Amer. Rhododendron Society 39: 7074.
Mlchaux, A. (1803). Flora boreali-americana. Vol. 1. Facsimile, ed. Hafner Press, New York.
Millais, J. G. (1917). Rhododendrons and the various hybrids. Vol. 1. Longmans Green, London.
Mishler, B. D. (1985). The morphological, developmental, and phylogenetic basis of species concepts in bryophytes. Bryologist 88: 207214.
Mishler, B. D. & Donoghue, M. J. (1982). Species concepts: A case for pluralism. Syst. Zool. 31: 491503.
Mossman, F. D. (1977). The western azalea on Stagecoach Hill. Pacific Hort. 38: 2833.
Nakai, T. (1922). Trees and shrubs indigenous to Japan proper. Vol. 1. Seibido Shoten, Nihombashi. Tokyo.
Nakamura, M. (1931). Caryological studies on the genus Rhododendron. J. Soc. Trop. Agric, Tohuku Imperial Univ. 3: 103109.
Philipson, M. N. (1980). Cotyledons and Rhododendron classification. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf., pp. 7588. NY Bot. Garden, Bronx, NY.
Philipson, W. R. & Philipson, M. N. (1968). Diverse nodal types in Rhododendron. J. Arnold Arbor. 49: 193224.
Porter, T. C. (1889a). Notes on two Rhododendrons. Bull. Torrey Bot. Club 16: 220221.
Porter, T. C. (1889b). Flora of the Pocono Plateau. Rhodora 1: 182185.
Prince, M. (1978). Our wild eastern treasures: native azaleas. Amer. Hort. Mag. 57: 1317.
Radford, R. E., Ahles, H. E. & Bell, C. R. (1968). Manual of the vascular flora of the Carolinas. University of North Carolina Press, Chapel Hill.
Raven, P. H. (1975). The bases of angiosperm phylogeny: cytology. Ann. Missouri Bot. Gard. 62: 724764.
Rehder, A. (1921). A monograph of the azaleas of North America. In: Wilson, E. H. & Rehder, A.A monograph of azaleas. Publication of the Arnold Arboretum No. 9. Harvard University, Cambridge, Mass.
Rehder, A. (1947). Two new forms of Rhododendron roseum. Contr. Gray Herb. 165: 911.
Sargent, C. S. (1917). American azaleas and their hybrids. Rhododendron Soc. Notes 1: 119121.
Sax, K. (1930). Chromosome stability in the genus Rhododendron. Amer. J. Bot. 17: 247251.
Schneider, E. (1969). Azalea viscosa hybriden. Dendroflora 6: 5052.
Shinners, L. H. (1961). Rhododendron coryi, a new repent species from southeastern Texas. Castanea 26: 156157.
Shinners, L. H. (1962).Rhododendron nudiflorum and R. roseum (Ericaceae)—Illegitimate names. Castanea 27: 9495.
Seithe-Von Hoff, A. (1960). Die Haarformen der Gattung Rhododendron L. und die Möglichkeit ihrer taxonomischen Verwertung. Bot. Jahr. Syst. 79: 297393.
Seithe-Von Hoff, A. (1980). Rhododendron hairs and taxonomy. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf., pp. 89116. NY Bot. Garden, Bronx, NY.
Sims, J. (1815). Rhododendron calendulaceum var. crocea. Bot. Mag. 41: pi. 1721.
Skinner, H. T. (1952). Character patterns in the flowering azaleas of the southern U.S. Yearb. Amer. Philos. Soc. (1952): 177179.
Skinner, H. T. (1955). In search of native azaleas. Morris Arbor. Bull. 6: 110, 15–22.
Skinner, H. T. (1959). An evaluation of our eastern wild azaleas. Arbor. Bull. 22: 8081,106.
Skinner, H. T. (1961). Classification of the native American azaleas. Proc. Int. Rhododendron Conf., pp. 8186. [American Rhododendron Society, Portland, Oregon, May 11–14.]
Skinner, H. T. (1965). Chapter 21. Deciduous Species and Named Varieties. In: Lee, F. P.The azalea book, pp. 191228. Ed. 2. D. Van Nostrand, Princeton, New Jersey.
Skinner, H. T. (1971). America's native azaleas. Pl. & Gard. 27: 3035.
Sleumer, H. (1966). An account of Rhododendron in Malesia. Fl. Males, ser. 1,6: 473674.
Sleumer, H. (1980). Past and present taxonomic systems of Rhododendron based on macromorphological characters. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf., pp. 1926. NY Bot. Garden, Bronx, NY.
Small, J. K. (1903). Flora of the southeastern U.S. New York.
Sneath, P. H. A. & Sokal, R. R. (1973). Numerical taxonomy—the principles and practice of numerical classification. W. H. Freeman, San Francisco.
Solymosy, S. L. (1974). Notes on Rhododendron coryi Shinners. Bull. Amer. Rhododendron Soc. 28: 188189.
Solymosy, S. L. (1976). A treatise on azaleas. Louisiana Society for Horticultural Research, Vol. 4.
Spethmann, W. (1980). Flavonoids and carotenoids of Rhododendron flowers and their significance for the classification of the genus Rhododendron. In: Luteyn, J. & O'Brien, M. (eds) Contributions toward a classification of Rhododendron. Proc. Int. Rhododendron Conf., pp. 247275. NY Bot. Garden, Bronx, NY.
Stevens, P. F. (1970). A classification of the Ericaceae: subfamilies and tribes. J. Linn. Soc, Bot. 64: 153.
Stevens, P. F. (1980a). Evolutionary polarity of character states. Annual Rev. Ecol. Syst. 11: 333358.
Stevens, P. F. (1980b). A revision of the Old World species of Calophyllum (Guttiferae). J. Arnold Arbor. 61: 117690.
Steward, A. N. (1958). Manual of vascular plants of the lower Yangtze Valley, China. Oregon State College, Corvallis, OR.
Swofford, D. (1993). PAUP: Phylogenetic analysis using parsimony, version 3.1.1. Computer program distributed by the Illinois Natural History Survey, Champaign, Illinois.
Szafer, W. (1975). General plant geography. Naukowe, Warsaw. (Translated from Polish by Massey, Helen M. for the Smithsonian Institution.)
Valckenier-Suringar, J. (1904). Azalea mollis und Azalea sinensis. Mitt. Deutsch. Dendrol. Ges. 13: 5354.
Valckenier-Suringar, J. (1908). Azalea mollis und Azalea sinensis. Gartenflora 57: 505517, pls 1575–1576.
Watrous, L. E. & Wheeler, Q. D. (1981). The out-group comparison method of character analysis. Syst. Zool. 30: 111.
Watson, L. (1964). The taxonomic significance of certain anatomical observations on Ericaceae, the Ericoideae, Calluna and Cassiope. New Phytol. 63: 274280.
Watson, L. (1965). The taxonomic significance of certain anatomical variations among Ericaceae. J. Linn. Soc. Bot. 59: 111121.
Weatherby, C. A. & Griscom, L. (1934). Notes on the spring flora of the coastal plain of South Carolina north of Georgetown. Rhodora 36: 2854.
Weigand, K. M. (1924). Some changes in nomenclature. Rhodora 26: 15.
Wldrlechner, M. P., Pellett, H. M. & Ascher, P. D. (1984). Observations on phylogenetic relationships between Rhododendron calendulaceum and R. bakeri. J. Rhododendron Species Found. 1:4963.
Wilbur, R. L. (1976). Illegitimate names Rhododendron nudiflorum (L.) Torr. and R. roseum (Loisel.) Rehder. Taxon 25: 178179.
Wiley, E. O. (1981). Phylogenetics: the theory and practice of phylogenetic systematics. Wiley, New York.
Willdenow, C. L. (1811). Berlinische Baumzucht oder Beschreibung der in Königlichen botanischen Garten bei Berlin im Freien ausdauernden. G. C. Nauck, Berlin.
Willingham, F. F., Jr (1973). A biosystematic study of bloom forms of Rhododendron calendulaceum. PhD Dissertation. Wake Forest University.
Willingham, F. F., Jr (1974). Variation in Rhododendron calendulaceum (Michx.) Torr. (Ericaceae) of the Nantahala Mountains, North Carolina. ASB Bull. 21: 9091.
Willingham, F. F., Jr (1975). Taxonomy of the flowering forms of Rhododendron calendulaceum. Bull. Amer. Rhododendron Soc. 29: 183186.
Willingham, F. F., Jr (1976). Variation and phenological forms in Rhododendron calendulaceutn. Castanea 41: 215223.
Wilson, E. H. (1921). A monograph of azaleas of the Old World. In: Wilson, E. H. & Rehder, A.A monograph of azaleas, pp. 1106. Publication of the Arnold Arboretum No. 9. Harvard University, Cambridge, Mass.
Wilson, E. H. & Rehder, A. (1921). A monograph of azaleas. Publication of the Arnold Arboretum No. 9. Harvard University, Cambridge, Mass.
Wishart, D. (1975). CLUSTAN Version 2.1. User's manual. University College London.
Wood, C. E. (1961). The genera of Ericaceae in the southeastern United States. J. Arnold Arbor. 42: 1080.
Wood, C. E. (1970). Some floristic relationships between the southern Appalachians and western North America. In: Holt, P. C. (ed.) The distributional history of the biota of the southern Appalachians. Part II: Flora. Research Division Monograph 2, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Edinburgh Journal of Botany
  • ISSN: 0960-4286
  • EISSN: 1474-0036
  • URL: /core/journals/edinburgh-journal-of-botany
Please enter your name
Please enter a valid email address
Who would you like to send this to? *
×

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed