Ulmus 'Morton'

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Ulmus hybrid
'Accolade', Morton Arboretum, Illinois
'Accolade', Morton Arboretum, Illinois
Hybrid parentage
U. davidiana var. japonica × U. davidiana var. japonica f. wilsoniana
Cultivar
'Morton'

Accolade™
Origin
USA

'Morton' (Accolade™) is an elm cultivar derived from a hybrid planted at the Morton Arboretum in 1924, which itself originated as seed collected from a tree at the Arnold Arboretum in Massachusetts. Although this tree was originally identified as Ulmus crassifolia, it is now is believed to have been a hybrid of the Japanese Elm Ulmus davidiana var. japonica and Wilson's Elm, the latter now sunk as another form of Ulmus davidiana var. japonica.[1]

The tree at the Morton Arboretum was noted for the resemblance of its habit to the American Elm Ulmus americana, its upright-arching branches creating the familiar vase-shape. Moreover, in its 80+ years it had survived three epidemics of Dutch Elm Disease there unscathed.[2] However, two trees included in trials at the University of Minnesota were found to be afflicted by the diease in 2004, although one appears to have recovered completely.[3] 'Morton' has now been cloned and promoted by the Chicagoland Grows corporation as a potential substitute for the innumerable American Elms lost to disease, although the tree does not grow as large as the iconic native elm, reaching scarcely 20 m at maturity; its glossy, deep green leaves are also markedly smaller.

'Morton' is reputed to grow well in almost all soils save those excessively wet, and is notably drought-tolerant and cold hardy. In artificial freezing tests at the Morton Arboretum [4] the LT50 (temp. at which 50% of tissues die) was found to be - 35.5 °C.

The tree grows vigorously at first, gaining as much as one metre per annum, but slows to approximately half that rate with maturity. Thus, a typical 20 year-old tree could be expected to have reached 14 m in height with a crown about 5 m in width.[5]

'Morton' has also proved to be highly resistant to elm yellows and the elm leaf beetle. It is currently being evaluated in the National Elm Trial [2] coordinated by Colorado State University.

Specimens grown from selfed seeds are featured in the Butterfly Conservation elm trials in Hampshire, England, where they have grown with extraordinary vigour, and proven very tolerant of local conditions, notably waterlogged soils in winter.[6]

Contents

[edit] Hybrid cultivars

'Morton' (Accolade™) was crossed with the hybrid cultivar 'Morton Plainsman' (Vanguard™). A selection of the resultant seedlings was marketed under the name 'Charisma', later changed to 'Morton Glossy' (Triumph™).

[edit] Arboreta etc. accessions

North America
Europe

[edit] Nurseries

North America
Europe

[edit] Synonymy

  • Thornhill Elm: Anon.

[edit] References

  1. ^ Fu, L., Xin, Y. & Whittemore, A. (2002). Ulmaceae, in Wu, Z. & Raven, P. (eds) Flora of China, Vol. 5 (Ulmaceae through Basellaceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, USA.[1]
  2. ^ Ware, G. Morton Arb. Quarterly, 28(1): 1-5, 1992.
  3. ^ Giblin, C. P. & Gillman, J. H. (2006). Elms for the Twin Cities: A Guide for Selection and Maintenance. University of Minnesota.
  4. ^ Shirazi, A. M. & Ware, G. H. (2004). Evaluation of New Elms from China for Cold Hardiness in Northern Latitudes. International Symposium on Asian Plant Diversity & Systematics 2004, Sakura, Japan.
  5. ^ Guries, R. P. & Smalley, E. B., (1986), Proc. Third Nat. Urban Forestry Conf., pp 214–218, 1986, Orlando, Florida.
  6. ^ Brookes, A. H. (2006). An evaluation of disease-resistant hybrid and exotic elms as larval host plants for the White-letter Hairstreak butterfly Satyrium w-album, Part 1. Butterfly Conservation, Lulworth, UK.

[edit] External links