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. The trees can live for several hundred years. It is a very hardy species that can ...

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

''Ulmus americana'' 'Jefferson' was cloned from a tree growing near a path in front of the

Freer Gallery of Art The Freer Gallery of Art is an art museum of the Smithsonian Institution in Washington, D.C. focusing on Asian art. The Freer and the Arthur M. Sackler Gallery together form the National Museum of Asian Art in the United States. The Freer and ...

, close to the

Smithsonian Institution Building The Smithsonian Institution Building, more commonly known as the Smithsonian Castle or simply The Castle, is a building on the National Mall housing the Smithsonian Institution's administrative offices and information center. Built as the first ...

("The Castle") on the

National Mall The National Mall is a Landscape architecture, landscaped park near the Downtown, Washington, D.C., downtown area of Washington, D.C., the capital city of the United States. It contains and borders a number of museums of the Smithsonian Institu ...

Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...

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

National Park Service The National Park Service (NPS) is an List of federal agencies in the United States, agency of the Federal government of the United States, United States federal government, within the US Department of the Interior. The service manages all List ...

, 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). In 2005, the Park Service and the

Agricultural Research Service The Agricultural Research Service (ARS) is the principal in-house research agency of the United States Department of Agriculture (USDA). ARS is one of four agencies in USDA's Research, Education and Economics mission area. ARS is charged with ext ...

(ARS) of the

United States Department of Agriculture The United States Department of Agriculture (USDA) is an executive department of the United States federal government that aims to meet the needs of commercial farming and livestock food production, promotes agricultural trade and producti ...

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 Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

: ''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 two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

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 two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

American Elm and an unknown

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

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 ...

)'' feeding during a 2009—2010 survey at an Oklahoma

arboretum An arboretum (: arboreta) is a botanical collection composed exclusively of trees and shrubs of a variety of species. Originally mostly created as a section in a larger garden or park for specimens of mostly non-local species, many modern arbor ...

. 'Jefferson' is susceptible to elm yellows

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-li ...

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 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. 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 Ceremonial counties of England, ceremonial county in South East England. It is bordered by Essex across the Thames Estuary to the north, the Strait of Dover to the south-east, East Sussex to the south-west, Surrey to the west, and Gr ...

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 Northwestern Europe, off the coast of European mainland, the 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, 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, Spalding,

Lincolnshire Lincolnshire (), abbreviated ''Lincs'', is a Ceremonial counties of England, ceremonial county in the East Midlands and Yorkshire and the Humber regions of England. It is bordered by the East Riding of Yorkshire across the Humber estuary to th ...

, 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