Ulmus americana 'Jefferson' | |
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Species | Ulmus americana |
Cultivar | 'Jefferson' |
Origin | National Park Service, US |
The American Elm cultivar Ulmus americana 'Jefferson' was cloned from a tree growing near a path in front of the Freer Gallery of Art, close to the Smithsonian Institution Building ("The Castle") on the National Mall in Washington, D.C. [1] The United States National Park Service, which had planted the tree during the 1930s, cloned it in 1993 after screening tests showed that it possessed an outstanding level of tolerance to Dutch elm disease (DED). [1]
In 2005, the Park Service and the Agricultural Research Service (ARS) of the United States Department of Agriculture jointly released the clone (formerly NPS 3–487) to the nursery trade as 'Jefferson'. [1] The parent tree appears to have remained unscathed by DED in 2014.
'Jefferson' is distinguished by its low, spreading form with arching limbs and broad U-shaped crotches. [2] The parent tree on the National Mall has reached a height of about 68 feet (20.7 m) after 80 years. Ploidy: 2n = 42.
Early studies on the parent tree found that the tree has triploid chromosomes, suggesting that it may be a hybrid between the tetraploid American Elm and an unknown diploid species. [3] A genetic study that the ARS conducted on the clone at the United States National Arboretum in Washington, D. C., during 2004 confirmed the tree as Ulmus americana, despite having some atypical features. [4]
A subsequent ARS study also confirmed that the tree is a triploid. The study's investigators concluded that a crossing of two American Elms, one a tetraploid, the other a less common diploid, had created the tree. The investigators found no triploids among the 81 wild trees that they sampled. [5]
The tree proved highly resistant to Dutch elm disease in an ARS trial (as clone N 3487/NA 62001). [6] NA 62001 showed little damage from elm leaf beetle (Xanthogaleruca luteola) feeding during a 2009—2010 survey at an Oklahoma arboretum. [7] 'Jefferson' is susceptible to elm yellows phytoplasma infection, as are other U. americana DED-resistant cultivars and native trees of that species. [8]
The Japanese beetle (Popillia japonica) highly prefers U. americana when feeding. [9] Verticillium wilt had a greater effect on U. americana than it had on all other elms studied in an investigation of that fungal disease. [10]
'Jefferson' has not been widely tested beyond Washington D.C. National Elm Trial results were inconclusive and provided no data on ‘Jefferson’ because of an early error in tree identification that occurred in the nursery trade. [11] [12] The error may still be causing nurseries to sell 'Princeton' elms that are mislabeled as 'Jefferson', although one can distinguish between the two cultivars as the trees mature. [11] [13] The Golden Hill Nursery in Kent introduced 'Jefferson' to the United Kingdom in 2010, but the clone remains rare in cultivation.
In 2005, the newest American elm—named Jefferson—was released jointly by ARS and the National Park Service (NPS), after collaborative screening tests by Townsend and James L. Sherald, NPS Natural Resource Officer, showed it to have an outstanding level of Dutch elm disease (DED) tolerance. It was cloned in 1993 from the original tree, a survivor of about 300 elms planted on the National Mall in Southwest Washington in the 1930s..
Triploid. May be a hybrid between tetraploid U. americana and an unknown diploid species.
(Jefferson's) identity has been questioned due to its disease tolerance, broad U-shaped branch unions, and bark, branch, and leaf characteristics..
To settle the question, the two scientists tested elm trees from across the species' eastern and central U.S. range. About 21 percent of the wild elms sampled were diploid; some grew in stands with tetraploids, while others were larger groupings of diploids..
The two ploidy levels grew in proximity to one another at several sites, east of the Appalachians and in eastern Missouri and west-central Oklahoma. Despite finding diploid and tetraploid trees growing near each other in several areas, no wild triploids were encountered.
Infection can be very destructive to some elms, particularly North American species. However, it is thought that European elm species tend to be much less affected than the highly susceptible American elm (U. americana)..
Consumers need to also be aware that a nursery trade mix-up a dozen years ago still plays out in the marketplace, and 'Princeton' elms continue to be sold as 'Jefferson' unknowingly by reputable nurseries from New York to Minnesota. .... National Elm Trial (NET) results were inconclusive and provided no data on 'Jefferson' due to the cultivar mix-up..
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical-montane regions of North America and Eurasia, presently ranging southward in the Middle East to Lebanon and Israel, and across the Equator in the Far East into Indonesia.
Ulmus americana, generally known as the American elm or, less commonly, as the white elm or water elm, is a species of elm native to eastern North America, naturally occurring from Nova Scotia west to Alberta and Montana, and south to Florida and central Texas, and is the State Tree of Massachusetts. The American elm is an extremely hardy tree that can withstand winter temperatures as low as −42 °C. Trees in areas unaffected by Dutch elm disease (DED) can live for several hundred years. A prime example of the species was the Sauble Elm, which grew beside the banks of the Sauble River in Ontario, Canada, to a height of 43 m (140 ft), with a d.b.h of 196 cm (6.43 ft) before succumbing to DED; when it was felled in 1968, a tree-ring count established that it had germinated in 1701.
Dutch elm disease (DED) is caused by a member of the sac fungi (Ascomycota) affecting elm trees, and is spread by elm bark beetles. Believed to be originally native to Asia, the disease was accidentally introduced into America, Europe, and New Zealand. In these regions it has devastated native populations of elms that did not have resistance to the disease. The name "Dutch elm disease" refers to its identification in 1921 and later in the Netherlands by Dutch phytopathologists Bea Schwarz and Christine Buisman, who both worked with professor Johanna Westerdijk. The disease affects species in the genera Ulmus and Zelkova, therefore it is not specific to the Dutch elm hybrid.
Ulmus 'Nanguen' is a complex fourth generation Dutch hybrid cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen. Lutèce was derived from the cross 'Plantyn' ×, an ancestry comprising four field elms, a wych elm, the curious Exeter Elm ('Exoniensis'), and a frost-resistant selection of the Himalayan elm.
Ulmus × hollandica 'Commelin' is a Dutch hybrid cultivar released for sale in 1960. The tree was raised at Baarn as clone 274 by the Foundation Willie Commelin Scholten Phytopathological Laboratory in 1940, from a crossing of Ulmus × hollandica 'Vegeta' and clone 1, an Ulmus minor selected from a 1929 elm seedlings lot obtained from the Barbier nursery, Orléans.
The Dutch hybrid elm cultivar Ulmus × hollandica 'Groeneveld' was cloned in 1949 at the De Dorschkamp Institute, Wageningen, and released in 1963 in response to the earlier, less virulent form of Dutch elm disease that afflicted Europe shortly after the First World War. The cultivar was derived from a crossing of Dutch clones '49', and '1', a Field Elm Ulmus minor found in central France and marketed by the Barbier nursery in Orléans.
The Siberian elm cultivar Ulmus pumila 'Green King' was once believed to have been derived from a crossing of the Siberian Elm Ulmus pumila with the American Red Elm Ulmus rubra. However, it is now apparent the tree originated as a sport of U. pumila in 1939 at the Neosho Nurseries, Neosho, Missouri.
Ulmus 'Columella' is a Dutch elm cultivar raised by the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen. Originally thought to have been derived from a selfed or openly pollinated seedling of the hybrid clone 'Plantyn', DNA analysis later determined it arose from a cross of 'Plantyn' and Ulmus minor. Sown in 1967, it was released for sale in 1989 after proving extremely resistant to Dutch elm disease following injection with unnaturally high doses of the pathogen, Ophiostoma novo-ulmi. However, propagated by grafting onto wych elm rootstocks, graft failure owing to incompatibility has become a common occurrence in the Netherlands.
Ulmus 'Exoniensis', the Exeter elm, was discovered near Exeter, England, in 1826, and propagated by the Ford & Please nursery in that city. Traditionally believed to be a cultivar of the Wych Elm U. glabra, its fastigiate shape when young, upward-curving tracery, small samarae and leaves, late leaf-flush and late leaf-fall, taken with its south-west England provenance, suggest a link with the Cornish Elm, which shares these characteristics.
The Field Elm cultivar Ulmus minor 'Christine Buisman' was the first cultivar released by the Dutch elm breeding programme, initiated in response to the less virulent form of Dutch elm disease (DED), Ophiostoma ulmi, which afflicted Europe's elms after the First World War. 'Christine Buisman' was selected from a batch of 390 seedlings grown from seed collected in the Parque de la Quinta de la Fuente del Berro, Madrid, by Mrs Van Eeghen, a friend of elm researcher Johanna Westerdijk, in 1929 and named for the elm disease researcher Christine Buisman. Originally identified as Ulmus foliacea, it was later treated as Ulmus × hollandica by Melville. However, more recent research in Belgium using DNA markers has reaffirmed 'Christine Buisman' as a clone of U. minor.
The American Elm cultivar Ulmus americana 'Princeton' was originally selected in 1922 by New Jersey nurseryman William Flemer of Princeton Nurseries for its aesthetic merit. 'Princeton' was later found to have a moderate resistance to Dutch elm disease (DED).
The American elm cultivar Ulmus americana 'New Harmony' was raised by the Maryland Agricultural Research Service and released by the United States National Arboretum in 1995, along with 'Valley Forge'. 'New Harmony' proved the most successful U. americana cultivar in the US National Elm Trial, averaging a survival rate of 85.5% overall.
The American elm cultivar Ulmus americana 'American Liberty' is in fact a group of six genetically distinct cultivars under a single name, although they are superficially similar. The Liberty elm is reportedly suitable for street planting, being tolerant of de-icing salts and air pollution. However, examples included in 10-year trials at Atherton, California to evaluate replacements for Californian elms lost to disease did not perform well. The late Professor Eugene Smalley summarized 'American Liberty' as "not as resistant as the Asian hybrids, but it still has the look of a classic American Elm".
The American Elm cultivar Ulmus americana 'Washington', of unknown derivation, was sourced from Princeton Nurseries, Princeton, New Jersey, from 1985, and planted on the National Mall, Washington D.C. It was then selected by H. V. Wester of the U. S. National Park Service and introduced for trials as NPS 3-178. Santamour pointed out that as the historic Washington Elm had been propagated as 'Washington', NPS 3-178, if ever registered as a cultivar, would need a different cultivar name.
Ulmus 'Patriot' is a hybrid cultivar raised by the United States National Arboretum in 1980. Derived from a crossing of the American hybrid 'Urban' with the Wilson's Elm cultivar 'Prospector', 'Patriot' was released to commerce, free of patent restrictions, in 1993. Tested in the US National Elm Trial coordinated by Colorado State University, 'Patriot' averaged a survival rate of 85% after 10 years.
The American Elm cultivar Ulmus americana 'Moline' was cloned from a wild seedling transplanted to Moline, Illinois, from nearby Rock River Valley in 1903 and propagated from 1916 by the Klehm Nurseries, Arlington Heights, Illinois.
The American Elm cultivar Ulmus americana 'Vase' was selected and propagated in the early 20th century by the Klehm Nurseries, Arlington Heights, Illinois, who advertised it at first as Ulmus americana 'Urnii', 'Klehms' American Vase-Shaped Elm', listing it, along with its stablemate Ulmus americana 'Moline', as a "novelty" in 1926, and describing both in some detail. Its original cultivar name, 'Urnii' – doubtful Latin – was changed to 'Vase' by Klehms by the 1930s, the tree also featuring as 'Vase Elm' in the catalogues of the Plumfield Nurseries, Fremont, Nebraska, from 1926, along with Klehms' 'Moline'. Vaughan's of Chicago marketed both from 1927. The Naperville Nurseries of Naperville, Illinois, marketed it from 1929 as 'Klehmii', 'Vase Elm', also introducing Klehms' 'Moline' at the same time.
Ulmus 'Fiorente' is a hybrid cultivar elm derived from a crossing of the Siberian Elm Ulmus pumila clone 'S.10' from Lucca, Italy, with the Ulmus minor clone 'C.02' from Lungarno, Florence, by the Istituto per la Protezione delle Piante (IPP), part of the Italian National Research Council, in Florence. The tree is protected by Plant Breeders' Rights bestowed by the EU on 25 March 2010.
The American Elm cultivar Ulmus americana 'Deadfree' was listed by the Urban Forestry Administration (UFA) of the District Department of Transportation in Washington, D.C., as one of its "street trees" in 2008. However, the UFA currently has no documentation to support it, and thus the entry may be spurious.
Ulmus 'Morfeo' is a hybrid elm cultivar raised by the Istituto per la Protezione delle Piante (IPP), Florence, in 2000. 'Morfeo' arose from a crossing of the Dutch hybrid clone '405' and the Chenmou Elm, the latter a small tree from the provinces of Anhui and Jiangsu in eastern China, The '405' clone is a full sister of 'Groeneveld', a crossing of an English U. × hollandica and a French U. minor from the Barbier Nursery, Orléans.