Ulmus davidiana var. japonica 'Thomson'

Infobox Cultivar | name = "Ulmus davidiana" var. "japonica"
cultivar = 'Thomson'
origin = PFRA Nursery, Saskatchewan, CanadaThe Japanese Elm "Ulmus davidiana" var. "japonica" cultivar 'Thomson' is a tough, cold-resistant selection assessed by the Prairie Farm Rehabilitation Administration (PFRA) Nursery (now the AAFC-PFRA&E Shelterbelt Centre) at Indian Head, Saskatchewan, in the 1970s as part of its shelterbelt tree research. Lindquist, C. H. & Howe, J. A. G. (1979). Thomson Elm. "Canadian Journal of Plant Science" 59:1159] Schroeder, W. (1994). Genetic improvement for prairie tree plantings. "Journal of Arboriculture". 20(1), Jan. 1994. ] [http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=2601&Type=2] [http://fletcher.ces.state.nc.us/programs/nursery/metria/metria11/warren/elm.htm] Burdekin, D. A. & Rushforth, K. D. (Revised by Webber J. F. 1996). Elms resistant to Dutch elm disease. "Arboricultural Research Note "2/96. Arboricultural Advisory and Information Service, Alice Holt, Farnham, UK.] .

The tree was one of a number of Japanese Elms planted in an experimental shelterbelt at Indian Head in 1953. These shelterbelt trees were derived from seed taken from two openly-pollinated Japanese Elms obtained from Manchuria and planted at Indian Head in 1929. 'Thomson' attained a height of 8 m in 25 years, a rather modest performance compared with Siberian Elm "Ulmus pumila" and American Elm "Ulmus americana" grown at the same site. Nevertheless, the tree has proved exceptionally hardy.

Description

'Thomson' is distinguished by a single trunk bearing a vase-shaped crown, the branches forming strong wide-angled crotches; the bark is dark grey and deeply fissured. The twigs have diamond-shaped fissures that become more apparent on second-year wood, and occasionally sport corky wings. The leaves are borne on 1 cm-long petioles, and average 7.5 cm in length, dark green and glabrous; they are obovate to elliptic in shape, with the typical acuminate tip and oblique base. The leaves turn bright yellow in autumn. The samarae are obovate and deeply notched at the apex.

Pests and diseases

'Thomson' displayed a resistance to Dutch elm disease when inoculated by Dr E. S. Kondo of the Canadian Forestry Service, Sault Ste. Marie; the original tree still survives (2008) and has also proven resistant to elm leaf beetle "Xanthogaleruca luteola".

Cultivation

The tree was usually propagated by grafting on Siberian Elm seedlings. Commercially available in Saskatchewan in 1980, 'Thomson' is no longer in commercial cultivation owing to propagation restrictions imposed by the Canadian government which severely limited its potential market. 'Thomson' was never introduced to Europe or Australasia.

ynonymy

*'Thompson': In error for 'Thomson'.

Etymology

The tree was named for Mr W. B. Thomson, appointed director of PFRA in 1973.

References