Ulmus thomasii

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 Ulmus thomasii subsp. var.  Cork Elm, Rock Elm
Habit: tree
Height: to
Width: to
100ft 40ft
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Width: warning.png"" cannot be used as a page name in this wiki. to 40 ft
Lifespan: perennial
Exposure: sun
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Minimum Temp: °Fwarning.png"°F" is not a number.
USDA Zones: 2 to 9
Sunset Zones:
Flower features:
Ulmaceae > Ulmus thomasii var. ,

Ulmus thomasii Sarg., 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.[1] Its preferred habitat is moist but well-drained sandy loam, loam, or silt loam soil, mixed with other hardwoods; it is moderately shade-tolerant [1]. 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. Where forest-grown, the crown is cylindrical and upright with short branches, and is narrower than most other elms. Rock Elm is also unusual among elms in that it usually has a monopodial growth habit. [2]. 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.

The leaves are 5 - 10 cm long and 2 - 5 cm wide, oval to obovate with a round, symmetrical base and acuminate apex. 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 < 40 mm long two weeks before the leaves from March to May, depending on the tree's location. The fruit is a broad ovate samara 13 - 25 mm long covered with fine hair, notched at the tip, and maturing during May or June to form drooping clusters at the leaf bases. [3].

Standard Cyclopedia of Horticulture

Ulmus racemosa, Thomas, not Borkh. (U. Thomasii, Sarg.). Cork Elm. Rock Elm. Tree, attaining 100 ft., with short spreading branches, forming an oblong round-topped head: branchlets pubescent usually until the second year and mostly irregularly corky winged when older: buds acute, pubescent: lvs. oval to oblong-obovate, unequal at the base, shortly acuminate, sharply and doubly serrate, glabrous or somewhat rough above, pubescent beneath, 2-4 in. long: fls. in slender pendulous racemes; calyx with 5-8 exserted stamens: fr. oval or obovate, with a shallow notch at the apex, pale, pubescent, 1/2 – 3/4 in. long. Que. to Tenn., west to Neb.

The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.



Pests and diseases

Like most North American elms, the Rock Elm is very susceptible to Dutch elm disease.




  1. http://esp.cr.usgs.gov/data/atlas/little/ulmuthom.pdf
  2. Bean, W. J. (1981). Trees and shrubs hardy in Great Britain, 7th edition. Murray, London.
  3. White, J & More, D. (2003). Trees of Britain & Northern Europe. Cassell's, London.

External links

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