Ulmus americana 'Jefferson'

Infobox Cultivar | name = "Ulmus americana"
cultivar = 'Jefferson'
origin = National Park Service, USAThe American Elm "Ulmus americana" cultivar 'Jefferson' is a tree of unknown origin introduced by the U. S. National Park Service 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 in 2004 [http://www.elmpost.org/jeh905.pdf] questioned this supposition, and suggested that the cultivar is in fact tetraploid, like all other American Elms.

Description

'Jefferson' is distinguished by its low, spreading form, with arching limbs to a height of about 12 m.

Pests and diseases

The tree is reputedly tolerant of Dutch elm disease, and very resistant to the Elm Leaf Beetle "Xanthogaleruca luteola" [http://www.sunshinenursery.com/survey.htm] .

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 [http://treehealth.agsci.colostate.edu/research/nationalelmtrial/NET_Cultivars.htm] coordinated by Colorado State University. The tree is not known to have been introduced to Europe or Australasia.

Accessions

North America

*Bartlett Tree Experts [http://www.bartlett.com/au100.cfm] , acc. nos. 2001-255/6/7.
*Longwood Gardens, acc. no. 2002-0413.

Nurseries

North America

*Sunshine Nursery [http://www.sunshinenursery.com/elms.htm] , Clinton, Oklahoma
*The Botany Shop Garden Center [http://www.botanyshop.com/ValleyForge.htm] , Missouri

External links

* [http://www.elmpost.org/jeh905.pdf 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.