Ulmus americana 'Lewis & Clark' = Prairie Expedition
Prairie Expedition leaves, midsummer
|Cultivar||'Lewis & Clark' = Prairie Expedition™|
|Origin||North Dakota State University Research Foundation, USA|
The American Elm Ulmus americana cultivar 'Lewis & Clark' (selling name Prairie Expedition) is a relatively new development from the North Dakota State University (NDSU) Research Foundation breeding programme, released in 2004 to commemorate the 200th anniversary of the eponymous expedition . The cultivar was cloned from a tree discovered in 1994 along the Wild Rice River south west of Fargo, ND., where all those around it had succumbed to Dutch elm disease; the tree remains in perfect health (2008).
Prairie Expedition is distinguished in maturity by its broad umbrella crown and dark green foliage.  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 . The leaves are < 13 cm in length by 9 cm broad, coarsely-toothed, and with a 4 mm petiole.
Pests and diseases
Possession of an innate resistance to Dutch elm disease was suggested after inoculation with the causal fungus at the NDSU, however replication of the tests is considered too limited to be conclusive. No other specific information available, but the species generally is highly susceptible to Elm Yellows; it is also moderately preferred for feeding and reproduction by the adult Elm Leaf Beetle Xanthogaleruca luteola  , and highly preferred for feeding by the Japanese Beetle Popillia japonica    in the USA.
Prairie Expedition has been included in the National Elm Trial coordinated by Colorado State University. The tree is in commerce in the USA, and was introduced to the UK in 2008, and the Netherlands in 2010.
The tree is named for the Lewis & Clark prairie expedition of 1804.
- North Dakota State University, no details known.
- Great Fontley, Fareham, UK, Butterfly Conservation Elm trials plantation, Home Field, H1. One tree, planted 2008, height 3.2 m in 2013.
- Bylands Nurseries Ltd. , Kelowna, British Columbia, Canada.
- Patmore Nursery , Brandon, Manitoba
- Sun Valley Garden Centre , Eden Prairie, Minnesota
- Capps, T. K. (1996). Selection, propagation and inoculation of American Elms with potential Dutch elm disease resistance. MSc thesis, NDSU.
- Miller, F. and Ware, G. (2001). Resistance of Temperate Chinese Elms (Ulmus spp.) to Feeding of the Adult Elm Leaf Beetle (Coleoptera: Chrysomelidae). Journal of Economic Entomology 94 (1): 162-166. 2001. Entom. Soc. of America.
- Miller, F., Ware, G. and Jackson, J. (2001). Preference of Temperate Chinese Elms (Ulmus spp.) for the Feeding of the Japanese Beetle (Coleoptera: Scarabaeidae). Journal of Economic Entomology 94 (2). pp 445-448. 2001. Entom. Soc.of America.
- Brookes, A. H. (2012). Disease-resistant elm cultivars, Butterfly Conservation trials report, 2nd revision, 2012. Butterfly Conservation, Hants & IoW Branch, England. 
- Brookes, A. (2013). Great Fontley Elm Trial, 2013 Report. Butterfly Conservation, Lulworth, UK.
- http://ndsuresearchfoundation.org/Prairie%20Expedition-RFM-37.htm U. americana Lewis & Clark Prairie Expedition NDSU Plant Sciences Introduction.
- http://treehealth.agsci.colostate.edu/research/nationalelmtrial/NationalElmTrial.htm National Elm Trial