| Ulmus americana 'Lewis & Clark' =Prairie Expedition | |
|---|---|
 'Lewis & Clark', Boarhunt, UK, age 20 yrs | |
| Species | Ulmus americana |
| Cultivar | 'Lewis & Clark' |
| Marketing names | Prairie Expedition |
| Origin | North Dakota State University Research Foundation, US |
TheAmerican elmcultivarUlmus americana 'Lewis & Clark' (trade namePrairie Expedition) is a development from theNorth Dakota State University (NDSU) Research Foundation breeding programme, released in 2004 to commemorate the 200th anniversary of the eponymous expedition.[1] The cultivar was cloned from a tree discovered in 1994 along theWild Rice River south west ofFargo, North Dakota, where all those around it had succumbed toDutch elm disease; the tree remains in perfect health (2008).Prairie Expedition proved only moderately successful in the US National Elm Trial, averaging a survival rate of 62.6% overall, potentially due to environmental factors rather than susceptibility to Dutch elm disease.[2] Nevertheless,Prairie Expedition is considered the hardiest of the American Elm cultivars, able to survive inZone 3 (-40 to -34 Celsius).[3]
Prairie Expedition was introduced to the UK in 2008 by Hampshire & Isle of Wight Branch,Butterfly Conservation, as part of an assessment of DED-resistant cultivars as potential hosts of the endangeredWhite-letter Hairstreak.[4]
Prairie Expedition is distinguished in maturity by its broad umbrella crown and dark green foliage.[5] However, the tree was judged to have little ornamental value in the National Elm Trial .[3] The clone grows moderately quickly, averaging an increase of > 1 m in height per annum when young, reaching a height of <17 m in 25 to 30 years.[6] The leaves are < 13 cm in length by 9 cm broad, coarsely-toothed, and with a 4 mmpetiole.
Possession of an innate resistance to Dutch elm disease was suggested after inoculation with the causal fungus at the NDSU,[7] however replication of the tests is considered too limited to be conclusive. No other specific information available, but the species as a whole is highly susceptible toElm Yellows; it is also moderately preferred for feeding and reproduction by the adult Elm Leaf BeetleXanthogaleruca luteola,[8] and highly preferred for feeding by the Japanese BeetlePopillia japonica[9][10] in the United States.U. americana is also the most susceptible of all the elms toverticillium wilt.[11][10]
Prairie Expedition has been included in theNational Elm Trial coordinated byColorado State University. The tree is in commerce in the US, and was introduced to the UK from Canada byButterfly Conservation in 2008,[4] and thence to the Netherlands in 2010.
The tree is named for theLewis and Clark Expedition of 1804.