Ulmus thomasii
1945790
225577840
2008-07-14T11:48:06Z
Ptelea
936706
:''This article is about the tree. For the town in Wisconsin, see [[Rock Elm, Wisconsin]].''
{{Taxobox
| status = LC
| name = ''Ulmus thomasii''
| regnum = [[Plant]]ae
| divisio = [[flowering plant|Magnoliophyta]]
| classis = [[dicotyledon|Magnoliopsida]]
| ordo = [[Rosales]]
| familia = [[Ulmaceae]]
| genus = ''[[Ulmus]]''
| species = '''''U. thomasii'''''
| binomial = ''Ulmus thomasii''
| binomial_authority = [[Charles Sprague Sargent|Sarg.]]
| synonyms =
*Cork Elm. <small>Anon.</small>
*''Ulmus racemosa'' <small>('''not''' Borkh.) Thomas</small>
}}
'''''Ulmus thomasii''''' <small>Sarg.</small>, the '''Rock Elm''' or '''Cork Elm''', is a [[deciduous]] tree native primarily to the [[Midwestern]] [[United States]]. The tree ranges from southern [[Ontario]] and [[Quebec]], south to [[Tennessee]], west to northeastern [[Kansas]], and north to [[Minnesota]].<ref> {{cite web | url = http://esp.cr.usgs.gov/data/atlas/little/ulmuthom.pdf | title = "Ulmus Thomasii Range Map" | accessdate = 2008-03-02 | publisher = [[United States Geological Survey]]}} </ref> Its preferred habitat is moist but well-drained sandy loam, loam, or silt loam soil, mixed with other [[hardwood|hardwoods]] [http://forestry.about.com/library/silvics/blsilulmtho.htm]. However, it also grows on dry uplands, especially on rocky ridges and [[limestone]] bluffs. The tree grows from 15-30 m tall and may live up to 300 years. It is moderately shade-tolerant. Like most North American elms, the Rock Elm is very susceptible to [[Dutch elm disease]].
[[Image: Rock Elm seedling.JPG|thumb|left|Seedling leaves]]
The [[leaf|leaves]] and are 5-10 cm long and 2-5 cm wide. They are asymmetrical with a round base and a tapering point, and have a hairy underside and incurved teeth. The leaf surface is shiny dark-green, turning bright yellow in [[autumn]]. The crown is cylindrical and upright with short branches, and is narrower most other elms. Rock Elm is also unusual among elms in that it usually has a [[monopodial]] growth habit. <ref name=Bean> Bean, W. J. (1981). ''Trees and shrubs hardy in Great Britain'', 7th edition. Murray, London. </ref>. 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 that the Rock Elm is sometimes called the Cork Elm. The petal-less, wind pollinated [[flower]]s are red-green and appear in racemes up to 40 mm long two weeks before the leaves from March to May, depending on the tree's location. The [[fruit]] is a broad egg-shaped key ([[Samara (fruit)|samara]]) 13-25 mm long covered with fine hair. They are notched at the tip, maturing during May or June to form drooping clusters at the leaf bases. <ref name=White>White, J & More, D. (2003). ''Trees of Britain & Northern Europe''. Cassell's, London.</ref>.
The [[wood]] 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, consequently it was once in great demand in America and Europe for a wide range of uses, notably [[shipbuilding]], [[furniture]], [[agricultural tools]], and [[musical instrument]]s. 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 2 mm a year. Over 250 annual growths were once counted in a log 24 cm square being sawn for [[gunwale]]s in an English boatyard, while a tree once grown at [[Kew Gardens]], [[London]], attained a height of only 12 m in 50 years <ref name=Elwes>Elwes, H. J. & Henry, A. (1913). ''The Trees of Great Britain & Ireland''. Vol. VII. pp 1848-1929. Private publication. [http://fax.libs.uga.edu/QK488xE4/7tgbi/]</ref>.
Wholly unsuited to the more temperate, maritime climate of northern Europe, the Rock Elm is extremely rare in cultivation across the Atlantic, although there have been unconfirmed reports of others in south-west [[Essex]], [[England]]. There are no known [[cultivar]]s of this taxon, nor is it known to be available from any nurseries.
==Arboreta accessions==
;North America
*[[Arnold Arboretum]], acc. no. 444-88.
*[[Brenton Arboretum]], [[Dallas Center]], [[Iowa]]. No details available.
*[[Morton Arboretum]], acc. no. 178-84, wild collected from [[Reedsville, Wisconsin]].
*[[Nebraska Statewide Arboretum]], no details available.
;Europe
*National Botanic Gardens [http://www.botanicgardens.ie], [[Glasnevin]], [[Dublin]], [[Eire]], location A3 (155)
*[[Royal Botanic Garden]] [[Wakehurst Place]] acc. no. 1968-48603.
==Etymology==
The tree was named in [[1902]] for [[David Thomas (civil engineer)|David Thomas]], an American civil engineer, who first identified the tree (as ''Ulmus racemosa'') in the early 19th century.
==See also==
*[[Dutch elm disease]]
==References==
{{reflist}}
[[Category:Ulmaceae|Elm, Rock]]
[[Category:Trees of Northeastern United States|Elm, Rock]]
[[Category:Trees of the Plains-Midwest (United States)|Elm, Rock]]
[[Category:Trees of New Hampshire|Elm, Rock]]
[[Category:Trees of Vermont|Elm, Rock]]
[[Category:Trees of Ontario|Elm, Rock]]
[[Category:Trees of Quebec|Elm, Rock]]