Ulmus 'Morton' Accolade

Ulmus hybrid cultivar

Accolade, Morton Arboretum, Illinois
Hybrid parentage U. davidiana var. japonica × U. davidiana var. japonica
Cultivar 'Morton' = Accolade™
Origin USA

Ulmus 'Morton' (selling name Accolade™) is an elm cultivar cloned from a putative intraspecific 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 Ulmus davidiana var. japonica.[1]

Description

The parent tree at the Morton Arboretum is noted for the resemblance of its habit to the American Elm Ulmus americana, its upright-arching branches creating the familiar vase-shape, 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, rarely exceeding 8 cm in length. The tree is commercially propagated by grafting onto an Ulmus pumila rootstock.

Accolade has a propensity to produce co-dominant stems and major branches with bark inclusions, demanding corrective pruning on at least an annual basis where planted in towns.[2]

Pests and diseases

In its 90+ years, the original tree at Morton has survived three epidemics of Dutch Elm Disease there unscathed.[3] However, two trees included in trials at the University of Minnesota were found to be afflicted by the disease in 2004, although one appears to have recovered completely.[4] The cultivar has also proved to be highly resistant to Elm Yellows and the elm leaf beetle Xanthogaleruca luteola [5] , but not to the Japanese Beetle, which can cause extensive foliar damage.[6]

Cultivation

Accolade 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 [7] 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.[8] Trees grown by Tollgate Education, Michigan State University, at Novi were the most vigorous and robust of the 37 different cultivars and species under assessment, described as looking like 'men among boys' . Accolade is being evaluated in the National Elm Trial coordinated by Colorado State University. Accolade was introduced to Europe in 2006 but is not in commerce there owing to patent restrictions.

Hybrid cultivars

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.

Synonymy

Accessions

North America
Europe

Nurseries

North America

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.
  2. ↑ Iles, J. (2009). Forget your fear of the elms. Western University website
  3. ↑ Ware, G. Morton Arb. Quarterly, 28(1): 1–5, 1992.
  4. ↑ Giblin, C. P. & Gillman, J. H. (2006). Elms for the Twin Cities: A Guide for Selection and Maintenance. University of Minnesota.
  5. ↑ McPherson, G. et al. (2008). National elm trial: Initial report from Northern California. Western Arborist, Fall 2009, 32–36.
  6. ↑ Brady, C., Condra, J., & Potter, D. (2008) Resistance of Landscape-suitable Elm (Ulmus spp.) Cultivars to Japanese Beetle, Leaf Miners, and Gall Makers. 2008 Research Report, Nursery & Landscape Program, 15–16. University of Kentucky.
  7. ↑ 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.
  8. ↑ Guries, R. P. & Smalley, E. B., (1986), Proc. Third Nat. Urban Forestry Conf., 214–218, 1986, Orlando, Florida.
  9. ↑ Photograph of autumn colouring of young 'Accolade' elms before Suzzallo Library: Arthur Lee Jacobson, 'Plant of the Month, 2008'
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