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Taxonomy of species in Rhododendron subsection Ledum
Kristian Theqvist, 14-Jan-2008, rev. 003

The inclusion of the ledum taxa in genus Rhododendron has led to some controversial naming issues. I have been somewhat confused on what names I should use in my documentation for the species and subspecies in subsection Ledum. I'll try now to clarify the situation by introducing a cross-reference table with Ledum names that are or have been in use. I made the table to guide in using valid names and to more easily match previously used names to the new ones.

Valid name in subsection Ledum of section Rhododendron subgenus Rhododendron genus Rhododendron
Other names that have been in use in various publications in subsection Ledum of genus Rhododendron
Old names in genus Ledum
Rhododendron tomentosum Harmaja, 1990.
R. tomentosum ssp. tomentosum
•  Used in the classification of genus Rhododendron by Chamberlain, D. et al., 1996.
R. tomentosum (Stokes) Harmaja, 1990.
•  An erroneous form.
R. palustre (L.) Kron & Judd, 1990.
•  An illegitimate later homonym.
Ledum tomentosum Stokes, 1812.
•  An illegitimate name.
L. palustre L. var. dilatatum Wahlenb., 1812.
L. palustre L., 1753.
R. subarcticum Harmaja, 1990.
R. tomentosum Harmaja ssp. subarcticum (Harmaja) Wallace, 1992.
  An illegitimate name that has been used in the classification of genus Rhododendron by Chamberlain, D. et al., 1996.
L. palustre L. ssp. decumbens (Ait.) Hultén, 1930.
L. decumbens (Aiton) Lodd. ex Steud, 1841.
L. palustre L. var. decumbens Aiton, 1789.
R. diversipilosum (Nakai) Harmaja, 1999.  
L. palustre L. ssp. diversipilosum (Nakai) H. Hara, 1956.
L. palustre L. var. diversipilosum Nakai, 1917. [basionym]
L. palustre L. var. nipponicum Nakai ?
L. nipponicum (Nakai) Tolm.
•  An illegitimate name.
R. groenlandicum (Oeder) Kron & Judd, 1990.  
L. palustre L. ssp. groenlandicum (Oeder) Hultén, 1948.
L. latifolium Jacq., 1789.
L. groenlandicum Oeder, 1771. [basionym]
R. hypoleucum (Kom.) Harmaja, 1990.  
L. hypoleucum Kom., 1916. [basionym]
R. neoglandulosum Harmaja, 1990.   L. glandulosum Nutt., 1843.
R. subulatum (Nakai) Harmaja, 2002.  
L. subulatum (Nakai) A.P.Khokhr. & Mazurenko, 1991.
L. palustre L. ssp. angustissimum Vorosch., 1978.
L. palustre L. var. angustum E. Busch. ?
L. palustre L. var. subulatum Nakai, 1917.
R. tolmachevii Harmaja, 1990.  
L. macrophyllum Tolm., 1953.
L. palustre L. var. yesoënse Nakai, 1922.?
L. maximum (Nakai) A.P.Khokhr. & Mazurenko, 1991. ?
L. palustre var. maximum Nakai, 1917. ?
R. ×columbianum (Piper) Harmaja, 1990.
•  Most probably R. groenlandicum × R. neoglandulosum.
 
L. columbianum Piper, 1906. [basionym]
L. glandulosum Nutt var. columbianum (Piper) Hitchc.
 
 
L. palustriforme A.P.Khokhr. & Mazurenko.

References
1. Harmaja, H. 1991. Taxonomic notes on Rhododendron subsection Ledum (Ledum, Ericaceae), with a key to its species. Ann. Bot. Fennici 28: 171-173.
2. Harmaja, H. 1999. Rhododendron diversipilosum, comb. nov. (Ericaceae). Ann. Bot. Fennici 35: 263-264.
3. Harmaja, H. 2002. Rhododendron subulatum, comb. nova (Ericaceae). Ann. Bot. Fennici 39: 183-184.
4. Kihlman, B. 2004. Hybrids Between Ledums and Lepidote Rhododendrons. J. Amer. Rhod Soc. 58(2):74-81
5. GRIN (Germplasm Resources Information Network) On-Line Taxonomy Database
6. Harri Harmaja's home page, http://www.fmnh.helsinki.fi/users/harmaja/