Ulmus thomasii

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.

Ulmus thomasii grows as a tree from {{convert|15|–|30|m|ft|round=5|abbr=on}} 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 [http://dendro.cnre.vt.edu/dendrology/syllabus/factsheet.cfm?ID=135], Natural Resources of Canada, tidcf.nrcan.gc.ca [https://tidcf.nrcan.gc.ca/images_web/imfc/arbres/photos/moyen/ulmus_thomosii_04.jpg] {{Webarchive|url=https://web.archive.org/web/20160802233957/http://tidcf.nrcan.gc.ca/images_web/imfc/arbres/photos/moyen/ulmus_thomosii_04.jpg |date=2016-08-02 }} [https://tidcf.nrcan.gc.ca/trees/factsheet/369] 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 [http://www.saylorplants.com/images/Ulmus/Ulmusthom_AAL01_SilvicsNorthAmerica_AH-654.jpg]

The leaves are {{convert|5|–|10|cm|in|0|abbr=on}} long and {{convert|2|–|5|cm|in|frac=4|abbr=on}} wide, oval to obovate with a round, symmetrical base and acuminate apex.{{Naturalis Biodiversity Center |id=WAG.1846088 }} U. thomasii leaves specimen, Quebec, 1932; {{Naturalis Biodiversity Center |id=L.1582468 }} 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 apetalous, wind-pollinated flowers are red-green and appear in racemes up to {{convert|40|mm|in|0|abbr=on}} long two weeks before the leaves from March to May, depending on the tree's location. The fruit is a broad ovate samara {{convert|13|–|25|mm|in|frac=32|abbr=on}} 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.{{cite journal|last=Hans|first=A. S.|year=1981|title=Compatibility and Crossability Studies in Ulmus|journal=Silvae Genetica|volume= 30|pages=4–5}}

File:The North American sylva; or, A description of the forest trees of the United States, Canada and Nova Scotia. Considered particularly with respect to their use in the arts and their introduction into (14778570501).jpg|U. racemosa [:U. thomasii] diagnostic illustration (1865)

File:A guide to the trees (Page 123) (8434849285).jpg|U. racemosa [:U. thomasii] diagnostic illustration (1900)

File:The tree book - A popular guide to a knowledge of the trees of North America and to their uses and cultivation (1920) (14782984355).jpg|U. thomasii shoot and buds (1920)

File:Ulmus thomasii (meisse) leaves 2.jpg|U. thomasii new leaves, Meisse

File:UlmusThomasii10.jpg|U. thomasii August leaves on short shoot, Jamesville, New York

File:SHHG Rock Elm leaf.jpg|U. thomasii leaves, Sir Harold Hillier Gardens, England

File:Ulmus thomasii (meisse) bark.jpg|U. thomasii bark, Meisse

File:UlmusThomasii17.jpg|U. thomasii young bark

File:Ulmus thomasii (meisse) corky wings.jpg|U. thomasii corky twig, Meisse

Ulmus thomasii is moderately shade-tolerant.{{Cite web | url=http://forestry.about.com/library/silvics/blsilulmtho.htm | title=Forestry}} Its preferred habitat is moist but well-drained sandy loam, loam, or silt loam soil, mixed with other hardwoods. However, it also grows on dry uplands, especially on rocky ridges and limestone bluffs.

Like most North American elms, U. thomasii is very susceptible to Dutch elm disease.

There are no known cultivars 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.[https://archive.org/details/CAT31287811/page/20 Kelsey, Frederick W., Choice Trees, cat. 55, N.Y. 1906, p.20][https://archive.org/details/CAT31330100/page/28/mode/2up Griffing's tree & plant book, 1929; Griffing's Interstate Nurseries, C.M. Griffing & Company;p.29][https://archive.org/details/CAT31332851/page/20/mode/2up 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.[https://plantnebraska.org/file_download/inline/42abc7e4-83d0-4273-bdbd-4cc25aae24fd 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 botanical gardens and arboreta, 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. Seedlings arising from crossings with Siberian elm (U. pumila) at the Lake States Forestry Experimental Station in the 1950s all perished,Sholtz, H. F. (1957). Rock Elm (Ulmus thomasii). Lake States Forest Experimental Station Paper 47:16. a classic case of hybrid lethality.{{Cite journal |doi = 10.1104/pp.006023|pmid = 12481061|pmc = 166689|title = Cell Death Processes during Expression of Hybrid Lethality in Interspecific F1 Hybrid between Nicotiana gossei Domin and Nicotiana tabacum|journal = Plant Physiology|volume = 130|issue = 4|pages = 1776–1787|year = 2002|last1 = Mino|first1 = Masanobu|last2 = Maekawa|first2 = Kenji|last3 = Ogawa|first3 = Ken'Ichi|last4 = Yamagishi|first4 = Hiroshi|last5 = Inoue|first5 = Masayoshi}}

The US National Champion, measuring {{convert|100|ft|m|abbr=on}} high in 1989, grows in Cass County, Michigan.{{cite web |publisher=American Forests |date=2012 |work=The 2012 National Register of Big Trees |title=Rock Elm (Ulmus thomasii) |url=http://www.americanforests.org/bigtree/rock-elm-ulmus-thomasii-3/}}

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, agricultural tools, 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 {{convert|2|mm|in|frac=32|abbr=on}} a year. Over 250 annual growth rings were once counted in a log {{convert|24|cm|in|frac=4|abbr=on}} square being sawn for gunwales in an English boatyard, while a tree once grown at Kew Gardens, London, attained a height of only {{convert|12|m|ft|abbr=on}} in 50 years.Elwes, H. J. & Henry, A. (1913). [http://fax.libs.uga.edu/QK488xE4/1f/trees_of_britain_and_ireland_vol_7.pdf The Trees of Great Britain & Ireland]. Vol. VII. 1848–1929. Republished 2004 Cambridge University Press, {{ISBN|978-1-108-06938-0}}

;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,{{Cite web | url=http://www.botanicgardens.ie |title = The National Botanic Gardens of Ireland}} Glasnevin, Ireland. Location: A3 (155)
• 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.

{{Commons category}}

{{Reflist}}

• [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233501331 U. thomasii, Flora of North America, www.efloras.org]
• [https://arboretum.harvard.edu/stories/ulmus-thomasii-the-hard-elm-thats-hard-to-find/ Brian Pruka, Ulmus thomasii: 'The Hard Elm That's Hard to Find', Arnoldia, Volume 74, Issue 1, 2016]

{{Elm species, varieties, hybrids, hybrid cultivars and species cultivars |state=collapsed}}

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thomasii

Category:Trees of Northern America

Category:Ulmus articles with images

Category:Elm species and varieties