Ulmus thomasii, the rock elm
Etymology
The tree was named in 1902 for David Thomas, an American
civil engineer who had first named and described the tree in 1831 as
Ulmus racemosa.
[This name had been used in 1800 for a different species of elm, hence the need for the later renaming that honored Thomas.]
Description
Ulmus thomasii grows as a tree from tall, and may live for up to 300 years. Where forest-grown, the crown is cylindrical and upright with short branches, and is narrower than most other elms.
[Photographs of mature Rock Elm showing narrow profile: Virginia Tech Department of Forest Resources [1], Natural Resources of Canada, tidcf.nrcan.gc.ca [2] [3]] Rock elm is also unusual among North American elms in that it is often
monopodial.
[Bean, W. J. (1981). Trees and shrubs hardy in Great Britain, 7th edition. Murray, London.] The bark is grey-brown and deeply furrowed into scaly, flattened ridges. Many older branches have 3–4 irregular thick corky wings. It is for this reason the rock elm is sometimes called the cork elm.
[Photograph of corky ridges of Rock Elm branches, Michigan State University Plant Encyclopedia [4]]
The leaves are long and wide, oval to obovate with a round, symmetrical base and acuminate apex.[ U. thomasii leaves specimen, Quebec, 1932; U. thomasii leaves specimen, Arnold Arboretum, 1960] The leaf surface is shiny dark green, turning bright yellow in autumn; the underside is pubescent. The perfect flower apetalous, wind-pollinated are red-green and appear in racemes up to long two weeks before the leaves from March to May, depending on the tree's location. The fruit is a broad ovate samara long covered with fine hair, notched at the tip, and maturing during May or June to form drooping clusters at the leaf bases.[White, J & More, D. (2003). Trees of Britain & Northern Europe. Cassell's, London.]
Although U. thomasii is protandrous, levels of self-pollination remain high.
[File:The diagnostic illustration (1865)]]
[File:A diagnostic illustration (1900)]]
Ecology
Ulmus thomasii is moderately shade-tolerant.
Its preferred habitat is moist but well-drained sandy loam, loam, or silt loam soil, mixed with other
. However, it also grows on dry uplands, especially on rocky ridges and
limestone bluffs.
Pests and diseases
Like most North American
,
U. thomasii is very susceptible to Dutch elm disease.
Cultivation
There are no known
of
Ulmus thomasii, nor is it known to be any longer in commerce. It appeared in some US nursery catalogues in the early 20th century.
[ Kelsey, Frederick W., Choice Trees, cat. 55, N.Y. 1906, p.20][ Griffing's tree & plant book, 1929; Griffing's Interstate Nurseries, C.M. Griffing & Company;p.29][ Griffing's tree & plant book, 1930; Griffing's Interstate Nurseries; p 20] It has, however, been planted as a street tree in Cheyenne, Wyoming, where in tight lines it keeps a monopodial habit recalling Jersey elm.
[ Justin Evertson, 'The Value of Large Trees', The Seed, Spring 2007, p.6, Nebraska Statewide Arboretum] The species is occasionally grown beyond its native range as a specimen tree in
and
arboretum, for example in northwestern Europe, but not commonly cultivated in northern Europe, being unsuited to the region's more temperate, maritime climate. However, the tree was propagated and marketed in the UK by the Hillier & Sons nursery, Winchester, Hampshire, from 1965 to 1977, during which time 49 were sold.
[Hillier & Sons (1977). Catalogue of Trees & Shrubs. Hillier, Ampfield, UK.][Hillier & Sons Sales inventory 1962 to 1977 (unpublished).]
Ulmus thomasii was crossed experimentally with Japanese elm ( U. davidiana var. japonica) at the Arnold Arboretum in Massachusetts, but no clones were released to commerce.[Sholtz, H. F. (1957). Rock Elm (Ulmus thomasii). Lake States Forest Experimental Station Paper 47:16.] a classic case of hybrid lethality.
Notable trees
The US National Champion, measuring high in 1989, grows in Cass County, Michigan.
Uses
The
wood of the rock elm is the hardest and heaviest of all elms, and where forest-grown remains comparatively free of knots and other defects. It is also very strong and takes a high polish, and consequently was once in great demand in America and Europe for a wide range of uses, notably
boatbuilding,
furniture,
agriculture, and musical instruments.
Much of the timber's strength is derived from the tight grain arising from the tree's very slow rate of growth, the trunk typically increasing in diameter by less than a year. Over 250 annual growth rings were once counted in a log square being sawn for in an English boatyard, while a tree once grown at Kew Gardens, London, attained a height of only in 50 years.[Elwes, H. J. & Henry, A. (1913). The Trees of Great Britain & Ireland . Vol. VII. 1848–1929. Republished 2004 Cambridge University Press, ]
Accessions
- North America
-
Arnold Arboretum, Massachusetts, US. Acc. no. 444-88.
-
Brenton Arboretum, Dallas Center, Iowa, US. No acc. details available.
-
Dominion Arboretum, Ottawa, Canada. No acc. details.
-
Morton Arboretum, Illinois, US. Acc. no. 178-84, wild collected from Reedsville, Wisconsin; 843-2005 (Kelleys Island, Erie County, Ohio); 122-2006 (Dixon County, Nebraska).
-
Nebraska Statewide Arboretum, US. No details available.
- Europe
-
Grange Farm Arboretum, Lincolnshire, UK. Acc. no. 706.
-
National Botanic Garden of Belgium, Meise, Belgium. Acc. no. 19800105.
-
National Botanic Gardens, Ireland,
-
Sir Harold Hillier Gardens, Hampshire, UK. Acc. no. 2008.0419, wild collected in Ontario, Canada, by Kristl Walek
-
Wakehurst Place Garden Wakehurst Place, UK. Acc. no. 1968-48603.
External links
