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Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 54, Number 2
Spring 2000

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Those Exciting Rhododendron Epidermal Appendages
Part III: Subgenus Hymenanthes
Arthur P. Dome
Seattle, Washington

This issue presents the interesting indumentum on the leaves of eight more popular members of the Subgenus Hymenanthes and their taxonomic classification.

Part I in the fall issue of the Journal (Vol. 53, Number 4, Fall 1999) illustrates and describes some of the different types of hairs and indumentum found on the leaves of this subgenus. Part I covers the functions of these appendages as well. Even with the new developments in DNA technology epidermal appendages are still very important in classifying these plants.

The photographs of the leaves in this Part III, as those in Part I and II, were taken from plants growing in the Rhododendron Species Botanical Garden in Federal Way, Washington. The magnification varies from X10 to X50.

Underside of mature new leaf of 
R. falconeri    Underside of mature new leaf of 
R. degronianum ssp*. degronianum
R. falconeri, S. Ponticum, Ss. Falconera. Mature new leaf underside with a bistrate
indumentum of funnel-shaped hairs over a thin layer of rosulate hairs.
Photo by Arthur P. Dome
   R. degronianum ssp*. degronianum, S. Ponticum, Ss. Pontica. Mature new leaf
underside with thick bistrate indumentum of dendroid and rosulate hairs.
Photo by Arthur P. Dome
 
Underside of young leaf of 
R. forrestii ssp. forrestii    Underside of mature new leaf of
R. haematodes
R. forrestii ssp. forrestii Repens Group, S. Ponticum, Ss. Neriiffora.
Young leaf underside with sparsely floccose tomentum and young papillae.
Photo by Arthur P. Dome
   R. haematodes, S. Ponticum, Ss. Neriiflora.
Mature new leaf underside with woolly bistrate indumentum of dendroid and rosulate hairs.
Photo by Arthur P. Dome
 
Underside of young leaf of 
R. macabeanum with white tomentum    Underside of young leaf of 
R. macabeanum
R. macabeanum, S. Ponticum, Ss. Grandia.
Young leaf upperside with white tomentum that disappears when mature.
Photo by Arthur P. Dome
   R. macabeanum, S. Ponticum, Ss. Grandia.
Young leaf underside with thick woolly bistrate indumentum of ramiform and rosulate hairs.
Photo by Arthur P. Dome
 
Underside of mature new leaf of 
R. tsariense var. tsariense    Underside of mature new leaf of 
R. wasonii var. wasonii
R. tsariense var. tsariense, S. Ponticum, Ss. Lanata.
Mature new leaf underside with thick woolly indumentum of ramiform hairs.
Photo by Arthur P. Dome
   R. wasonii var. wasonii, S. Ponticum, Ss. Taliensia.
Mature new leaf underside with thick woolly indumentum of long rayed hairs.
Photo by Arthur P. Dome

Acknowledgments
The author is indebted to Steve Hootman, Co-Director-Curator, Rhododendron Species Foundation, Federal Way, Washington, for proofreading the text of this article.

References
1. Chamberlain, David, and Roger Hyam, George Argent, Gillian Fairweather, Kerry S. Walter. 1996. The Genus Rhododendron, Its classification & synonymy. Edinburgh: Royal Botanic Garden Edinburgh.
2. Cowan, John Macqueen. 1950. The Rhododendron Leaf. Edinburgh: Oliver and Boyd.
3. Cox, Peter A. and Kenneth, N.E., 1997. The Encyclopedia of Rhododendron Species, Glendoick Publishing.
4. Davidian, H. H. 1982. The Rhododendron Species, Vol. II. Elepidotes.. Portland, OR: Timber Press.
5. Davidian, H. H. 1992. The Rhododendron Species, Vol. III, Elepidotes, Portland, OR: Timber Press. 6. Cullen, J. 1980. Notes from the RBGE, Vol. 39,. Edinburgh: Royal Botanic Garden Edinburgh.

* S = Section, Ss = Subsection, ssp = Subspecies, var. = Variety, syn.= synonym.

Arthur Dome, a member of the Seattle Chapter, has written articles on alpine rhododendrons and ericaceous companions for the Journal. He will conclude this series on epidermal appendages in the next issue.


Volume 54, Number 2
Spring 2000

DLA Ejournal Home | JARS Home | Table of Contents for this issue | Search JARS and other ejournals