Validation of Botanical Names: Rhododendron brachycarpum
ssp. tigerstedtii and Rhododendron maximum var. leachii
Donald H. Voss
Rhododendron brachycarpum ssp. tigerstedtii
The subspecies tigerstedtii in Rhododendron brachycarpum was published by Nitzelius (distinguished curator of the dendrological section of the Göteborg Botanical Garden in Sweden) without explicit identification of its type (Nitzelius, 1970). With respect to the type (p. 210), Nitzelius stated only: "Holotypus im Herbarium des Botan. Gartens Göteborg." He provided no concrete reference to some detail (such as collector's name, collection number, or collection date) identifying the type specimen. Nitzelius thus failed to meet the requirements of the Botanical Code (Article 37.2) for valid publication (Greuter et al., 2000).
I here validate the name of Nitzelius' subspecies as Rhododendron brachycarpum D. Don ex G. Don ssp. tigerstedtii Nitz. ex D. H. Voss, with the type here designated: Sweden, Göteborg, Bot. trädg., Japandalen, maj 1969, T. Nitzelius s.n. This sheet is in the Göteborg University Botanical Institute Herbarium (GB), marked as the holotype for "Rhododendron brachycarpum D. Don ssp. tigerstedtii, Nitz. ssp. nova." The Latin diagnosis in Nitzelius, Deutsche Baumschule 1970(7):210 serves to complete the validation of this name. This conforms to Article 45.1 and closely parallels Example 2 of Article 45 of the Botanical Code (Greuter et al., 2000).
Davidian considered the rhododendron named for Dr. Tigerstedt to be a variety, not a subspecies. In treating the Ponticum Series, he included "brachycarpum D. Don ex G. Don var. tigerstedtii (Nitzelius) Davidian, comb. nov." (Davidian, 1989, 1992). But because the basionym (ssp. tigerstedtii Nitz.) was not validly published, Davidian's combination is not validly published.
The subspecies tigerstedtii, a native of central to northern Korea, has morphological characteristics that Nitzelius considered distinct from those of the Japanese subspecies. The differences are discussed in Nitzelius (1970), and summarized by Cox: [ssp. tigerstedtii] "is apparently larger in all parts...with thicker shoots, larger growth and larger leaves and flowers" (Cox, 1979).
The Edinburgh botanists (Chamberlain et al., 1996) apparently consider that the characteristics on which Nitzelius based his designation of ssp. tigerstedtii fall within the range of variation of R. brachycarpum ssp. brachycarpum. Accordingly, they list ssp. tigerstedtii as a synonym of ssp. brachycarpum. Whether one accepts this taxonomic judgment or prefers to maintain Nitzelius' name identifying a separate taxon important in horticulture, valid publication is required for nomenclatural recognition.
As to its value in horticulture, Nitzelius identified the most intriguing characteristic of ssp. tigerstedtii as its remarkable cold hardiness: it reportedly survived -45°C (-49°F) at the Mustila Arboretum in Finland without damage to leaves and flower buds (Nitzelius, 1970). This hardiness was seen as a key to expanded ornamental planting of broadleaved rhododendrons in areas beyond the usual cold-tolerance limits.
The prospect of developing rhododendrons that can thrive in colder climes has drawn continued attention to R. brachycarpum ssp. tigerstedtii. Porteous (1990) discusses experiences with both lepidote and elepidote rhododendrons near Toronto, Ontario. The article focuses on the breeding program of Dr. Joe Brueckner, who began his quest for cold hardy rhododendrons while living in St. John, New Brunswick, Canada, and later established a garden at Mississauga, near Toronto. Porteous comments that "All of the R. brachycarpum ssp. tigerstedtii crosses have proven to be leaf hardy in Mississauga and, with one or two exceptions, bud hardy."
A subsequent article in this journal (Tigerstedt & Uosukainen, 1996) not only describes the use of R. brachycarpum ssp. tigerstedtii in a large-scale breeding program in Finland but also discusses the critical importance of climate (continental, maritime) and latitude (daylength) in breeding for cold hardiness. It points out, for example, that in a "typical maritime rhododendron environment" ssp. tigerstedtii tends to break dormancy early and is subject to injury from spring frosts. As of 1996, eight cultivars from the breeding program had been named; six had ssp. tigerstedtii as the seed parent. One of the latter group, 'Elviira', is being used in Captain Steele's breeding program in Nova Scotia (Weagle, 2001).
Seeking other indications of current use of ssp. tigerstedtii in northern areas, I contacted John Weagle (Halifax, Nova Scotia). He kindly forwarded my inquiry by e-mail to friends in northern Europe and mailed me copies of their responses (I am a troglodyte who does not use a modem).
Dr. Tigerstedt (Professor emeritus, University of Helsinki, Finland) notes continuation of his work with a large seedling population of 1996 crosses using ssp. tigerstedtii. This program is directed toward developing a cold-hardy yellow rhododendron. He also states that "The tigerstedtii is easy to distinguish from the true brachycarpum on the basis of leaf length (longer), flower color (pure white), and growth habit (more treelike)."
Svend Aage Askjaer (Hvidbjerg, in NW Denmark) mentions that in 1981-82 mature plants of ssp. tigerstedtii and their flower buds tolerated -31°C (-24°F) but that several plants have been lost to bark split after severe fluctuations between mild weather and frost.
Kaarel Voitk (near Stockholm, Sweden) has made crosses between ssp. tigerstedtii (as seed parent) and about twenty other species and cultivars. He notes that in addition to cold hardiness, an advantage of ssp. tigerstedtii is its purity of color ("doesn't impart any magenta to its hybrids"). Among disadvantages, he mentions the need for a climate without large fluctuations between mild temperatures and frosts to avoid bark-split.
Rhododendron brachycarpum ssp. tigerstedtii has special qualities that recommend its use in selection and breeding programs for appropriate areas; it is not a panacea for cold-hardiness problems. Continued interest in exploiting the demonstrated qualities of this plant indicates a need to maintain a separate identity. Because of the wild origin of this plant, it is appropriate to use a botanical name for this purpose. It is to that end that I undertook validation of Nitzelius' name for the plant.
Rhododendron maximum var. leachii
The ARS Plant Names Registrar, Jay Murray, requested that I look into the nomenclatural status of Rhododendron maximum var. leachii. The trail begins with Leach, 1961. In his "Author's Acknowledgments," Leach states that "Mr. Bernard Harkness provided a technical Latin botanical description." This description appears on page 192 of the Leach book and is followed by a statement that "Herbarium specimens have been supplied to various herbaria, the type being in the Highland Park Herbarium at Rochester, N.Y." No identification of the type specimen was supplied. The case thus parallels that of R. brachycarpum ssp. tigerstedtii, in that the infraspecific epithet leachii was not validly published.
The staff of Highland Botanical Park Herbarium kindly furnished a xerographic copy of the type sheet for var. leachii. It is now possible to identify the type and validate Harkness' epithet leachii. (Mr. Kent Millham, propagator at the park, informs me that Bernard Harkness was taxonomist at the park from the late 1940s to 1963.)
I here validate the name of Harkness' variety as Rhododendron maximum L. var. leachii B. E. Harkn. ex D. H. Voss, with the type here designated: United States, Pennsylvania, Brookville, Garden, December 15, 1957, David Leach, s.n. The holotype sheet is in the Herbarium of Highland Botanical Park (HPH), Rochester, N.Y., marked as "TYPE SPECIMEN" for "Rhododendron maximum var. Leachii Hark." The Latin diagnosis in Leach, 1961, Rhododendrons of the World, p. 192 (footnote), serves to complete the validation of this name. The word "Garden" on the label of the type sheet implicitly refers to the garden of David Leach in Brookville, PA.
Chamberlain, David, et al. 1996. The Genus Rhododendron: Its classification & synonymy. Edinburgh: Royal Botanic Garden Edinburgh.
Cox, Peter. 1979. The Larger Species of Rhododendron. London: B. T. Batsford.
Davidian, H. H. 1989. The Rhododendron Species, Vol. II Elepidotes, Part 1 Arboreum - Lacteum. Portland, OR: Timber Press.
Davidian, H. H. 1992. The Rhododendron Species, Vol. III Elepidotes continued, Neriiflorum - Thomsonii, Azaleastrum and Camtschaticum. Portland, OR: Timber Press.
Greuter, W. et al. 2000. International Code of Botanical Nomenclature (St. Louis Code). Koenigstein, Germany: Koeltz Scientific Books.
Leach, David G. 1961. Rhododendrons of the World. New York: Charles Scribner's Sons.
Nitzelius, T. 1970. Rhododendron brachycarpum ssp. tigerstedtii, eine neue Unterart. Deutsche Baumschule 1970(7):207-212.
Nitzelius, T. 1973. Personal communication to Dr. T. R. Dudley, U.S. National Arboretum, forwarding a reprint of the Deutsche Baumschule article with corrections of "misprints" marked.
Porteous, Barrie. 1990. Rhododendrons in a cold climate. Jour. Amer. Rhod. Soc. 44(2):78-83.
Tigerstedt, Peter M. A. & Marjatta Uosukainen. 1996. Breeding cold-hardy rhododendrons. Jour. Amer. Rhod. Soc. 50(4):185-189.
Weagle, John. 2001. Breeding for dwarf elepidotes in Nova Scotia. Jour. Amer. Rhod. Soc. 55(1):6-8.
The author extends thanks to Prof. Uno Eliasson, Curator, Herbarium GB, Göteborg University, for providing a xerographic copy of the herbarium sheet deposited by Nitzelius at GB as the intended holotype for R. brachycarpum ssp. tigerstedtii; and to Dr. Alan Whittemore, taxonomist, U.S. National Arboretum, Dr. Joseph Kirkbride, taxonomist, USDA, Agricultural Research Service, and Dr. Dan Nicolson, Department of Botany, Smithsonian Institution for patient guidance. With respect to R. maximum var. leachii, I am indebted to Thomas S. Pollock and Kent Millham of the Highland Botanical Park, Rochester, N.Y., for a xerographic copy of the type sheet and information about Bernard Harkness. Any errors or infelicities remain the sole responsibility of the author.
Donald Voss, a member of the Potomac Valley Chapter, is a frequent contributor to the Journal on botanical nomenclature.