The

American Elm ''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 F ...

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...

''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 Smithsonian Institution Building, located near the National Mall in Washington, D.C. behind the National Museum of African Art and the Sackler Gallery, houses the Smithsonian Institution's administrative offices and information center. Th ...

("The Castle") on the National Mall in

Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...

(1) .
(2) .
(3
Sherald, 2009, pp. 37—38.
/ref> The United States

National Park Service The National Park Service (NPS) is an agency of the United States federal government within the U.S. Department of the Interior that manages all national parks, most national monuments, and other natural, historical, and recreational propert ...

, 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 Dutch elm disease (DED) is caused by a member of the sac fungi (Ascomycota) affecting elm trees, and is spread by elm bark beetles. Although believed to be originally native to Asia, the disease was accidentally introduced into Americas, America ...

(DED). In 2005, the Park Service and the Agricultural Research Service (ARS) of the

United States Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of com ...

jointly released the clone (formerly NPS 3–487) to the nursery trade as 'Jefferson'. The parent tree appears to have remained unscathed by DED in 2014.

Description

'Jefferson' is distinguished by its low, spreading form with arching limbs and broad U-shaped crotches. The parent tree on the National Mall has reached a height of about after 80 years. Ploidy: ''2n'' = 42.

Genetics

Early studies on the parent tree found that the tree has

triploid Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s, suggesting that it may be a hybrid between the

tetraploid Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...

American Elm and an unknown diploid species. A genetic study that the ARS conducted on the clone at the

United States National Arboretum The United States National Arboretum is an arboretum in northeast Washington, D.C., operated by the United States Department of Agriculture's Agricultural Research Service. It was established in 1927 by an act of Congress after a campaign by USDA ...

in Washington, D. C., during 2004 confirmed the tree as ''Ulmus americana'', despite having some atypical features. . 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.

Pests and diseases

The tree proved highly resistant to Dutch elm disease in an ARS trial (as clone N 3487/NA 62001). . NA 62001 showed little damage from elm leaf beetle ''(

Xanthogaleruca luteola ''Xanthogaleruca luteola'', commonly known as the elm-leaf beetle, is a beetle species in the family Chrysomelidae that is native to Europe but invasive in other parts of the world.http://cisr.ucr.edu/elm_leaf_beetle.html - Center for Invasive Sp ...

)'' feeding during a 2009—2010 survey at an Oklahoma arboretum. 'Jefferson' is susceptible to

elm yellows Elm yellows is a plant disease of elm trees that is spread by leafhoppers or by root grafts."Elm Yellows." Elmcare.Com. 19 Mar. 2008 . Elm yellows, also known as elm phloem necrosis, is very aggressive, with no known cure. Elm yellows occurs in th ...

phytoplasma Phytoplasmas are obligate intracellular parasites of plant phloem tissue and of the insect vectors that are involved in their plant-to-plant transmission. Phytoplasmas were discovered in 1967 by Japanese scientists who termed them mycoplasma-lik ...

infection, as are other ''U. americana'' DED-resistant cultivars and native trees of that species. The Japanese beetle ''( Popillia japonica)'' highly prefers ''U. americana'' when feeding.

Verticillium wilt Verticillium wilt is a wilt disease affecting over 350 species of eudicot plants. It is caused by six species of '' Verticillium'' fungi: ''V. dahliae'', ''V. albo-atrum'', ''V. longisporum'', ''V. nubilum'', ''V. theobromae'' and ''V. tricorp ...

had a greater effect on ''U. americana'' than it had on all other elms studied in an investigation of that fungal disease.

Cultivation

'Jefferson' has not been widely tested beyond

Washington D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, Na ...

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. . 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. . The Golden Hill Nursery in

Kent Kent is a county in South East England and one of the home counties. It borders Greater London to the north-west, Surrey to the west and East Sussex to the south-west, and Essex to the north across the estuary of the River Thames; it faces ...

introduced 'Jefferson' to the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

in 2010, but the clone remains rare in cultivation.

Accessions

North America

Bartlett Tree Experts
US. Acc. nos. 2001-255/6/7. *

Longwood Gardens Longwood Gardens is a botanical garden that consists of over 1,077 acres (436 hectares; 4.36 km2) of gardens, woodlands, and meadows in Kennett Square, Pennsylvania, United States in the Brandywine Creek Valley. It is one of the premier h ...

, US. Acc. no. 2002-0413. *

, US. Acc. nos. 76448, 76625, 57844.

Europe

Grange Farm Arboretum The Grange Farm Arboretum is a small private arboretum comprising 3 hectares accommodating over 800 trees, mostly native and ornamental species or cultivars, notably oaks, ashes, walnuts and elms, growing on a calcareous loam.Ostler, J. (2009) ...

Sutton St James Sutton St James is a village and civil parish in the South Holland district of Lincolnshire, England, about south-west of Long Sutton. Lying in the Lincolnshire Fens, Sutton St James did not exist at the time of the 1086 ''Domesday Book''. Su ...

, Spalding,

Lincolnshire Lincolnshire (abbreviated Lincs.) is a Counties of England, county in the East Midlands of England, with a long coastline on the North Sea to the east. It borders Norfolk to the south-east, Cambridgeshire to the south, Rutland to the south-we ...

, UK. Acc. no. not known.

Notes

External links

Review of current elm selections in the USA.

References

* . {{Elm species, varieties, hybrids, hybrid cultivars and species cultivars , state=collapsed American elm cultivar Ulmus articles with images Ulmus