The American Elm

American Elm

Ulmus americana, generally known as the American Elm or, less commonly, as the White Elm or Water Elm, is a species native to eastern North America, occurring from Nova Scotia west to Alberta and Montana, and south to Florida and central Texas. The American elm is an extremely hardy tree that can...

 Ulmus americana cultivar 'Jefferson' was cloned from a tree that grows along the National Mall

National Mall

The National Mall is an open-area national park in downtown Washington, D.C., the capital of the United States. The National Mall is a unit of the National Park Service , and is administered by the National Mall and Memorial Parks unit...

 in Washington D. C. http://www.botanyshop.com/OtherItems/JeffersonElmGallery/JeffersonElm8.htm. Planted in the 1930s, it remains unscathed by Dutch elm disease, and was cloned (NPS 3487) by the U. S. National Park Service

National Park Service

The National Park Service is the U.S. federal agency that manages all national parks, many national monuments, and other conservation and historical properties with various title designations...

, which released it as 'Jefferson' in 2004. Although early reports of studies on this clone had indicated that it had triploid chromosome levels (suggesting it may be a hybrid between the tetraploid American Elm and a diploid species), a genetic study performed by the United States National Arboretum

United States National Arboretum

The United States National Arboretum is an arboretum in Washington, D.C., operated by the United States Department of Agriculture's Agricultural Research Service as a division of the Henry A. Wallace Beltsville Agricultural Research Center...

 in 2004 http://www.elmpost.org/jeh905.pdf confirmed the tree as an American Elm, despite its atypical features.

Description

'Jefferson' is distinguished by its low, spreading form with arching limbs and broad U-shaped crotches; the tree ultimately reaching a height of about 12 m (40 ft).

Pests and diseases

The tree proved highly resistant to Dutch elm disease

Dutch elm disease

Dutch elm disease is a disease caused by a member of the sac fungi category, affecting elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native...

 in USDA trials (as clone N 3487/NA 62001) , and very resistant to the Elm Leaf Beetle Xanthogaleruca luteola

Xanthogaleruca luteola

Xanthogaleruca luteola, commonly known as the Elm Leaf Beetle, is a serious pest of the elm. Indigenous to Europe, it was accidentally introduced to North America. Both the imagines and larvae feed on the emergent leaves of the elm...

http://www.sunshinenursery.com/survey.htm. No specific is information available, but the species generally is highly susceptible to Elm Yellows

Elm Yellows

Elm Yellows is a plant disease of elm trees that is spread by leafhoppers or by root grafts. Elm Yellows, also known as Elm Phloem Necrosis, is very aggressive, with no known cure. Elm Yellows occurs in the Eastern United States and southern Ontario in Canada. It is caused by phytoplasmas which...

 and highly preferred for feeding by the Japanese Beetle Popillia japonica http://www.bioone.org/doi/full/10.1603/0022-0493%282001%29094%5B0445%3APOTCEU%5D2.0.CO%3B2 http://www.sunshinenursery.com/survey.htm in the USA.
U. americana is also the most susceptible of all the elms to verticillium wilt

Verticillium wilt

Verticillium Wilt is a wilt disease of over 300 species of eudicot plants caused by one of two species of Verticillium fungus, V. dahliae and V. albo-atrum. Many economically important plants are susceptible including cotton, tomatoes, potatoes, eggplants, peppers and ornamentals, as well as others...

 .

Cultivation

Neither 'Jefferson' nor the cultivar 'Washington' has been widely tested beyond Washington D.C., although it is now being evaluated in the National Elm Trial

National Elm Trial

The National Elm Trial is an American volunteer effort to evaluate a range of newly developed elm cultivars as replacements for elms destroyed by Dutch elm disease...

 coordinated by Colorado State University

Colorado State University

Colorado State University is a public research university located in Fort Collins, Colorado. The university is the state's land grant university, and the flagship university of the Colorado State University System.The enrollment is approximately 29,932 students, including resident and...

. The tree was introduced to the UK in 2010.

North America

• Bartlett Tree Experts http://www.bartlett.com/au100.cfm. Acc. nos. 2001-255/6/7.
• Longwood Gardens
  Longwood Gardens
  Longwood Gardens consists of over 1,077 acres of gardens, woodlands, and meadows in Kennett Square, Pennsylvania, United States in the Brandywine Creek Valley...
  
  . Acc. no. 2002-0413.
• U S National Arboretum
  United States National Arboretum
  The United States National Arboretum is an arboretum in Washington, D.C., operated by the United States Department of Agriculture's Agricultural Research Service as a division of the Henry A. Wallace Beltsville Agricultural Research Center...
  
   http://www.usna.usda.gov/index.htm, Washington, D.C.
  Washington, D.C.
  Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....
  
  , USA. Acc. nos. 76448, 76625, 57844.

External links

• DNA Fingerprinting of Clones and Hybrids of American Elm and Other Elm Species with AFLP Markers. Summary of a genetic study which suggests strongly that the Jefferson elm is tetraploid.
• http://www.elmpost.org/2005-02.htm Photograph showing the mature form of the Jefferson elm.
• http://www.sunshinenursery.com/elms.htm Review of current elm selections in the USA.
• http://fletcher.ces.state.nc.us/programs/nursery/metria/metria11/warren/elm.htm Return of the Elm -the status of elms in the nursery industry in 2000. Warren, K., J. Frank Schmidt and Co.