rock elm

(Ulmus thomasii)

Conservation Status


No image available

  IUCN Red List

not listed


NNR - Unranked

SNR - Unranked


not listed

Wetland Indicator Status
  Great Plains

FACU - Facultative upland


FAC - Facultative

  Northcentral & Northeast

FAC - Facultative


Rock elm is a fast growing deciduous tree in the White Elm group. In Minnesota mature trees are usually 40 to 60 tall and 12 to 24 in diameter at breast height. Large individuals can be over 100 in height and 60 in diameter. It was once a long-lived tree, up to 200 years. However, the wilt fungus Dutch Elm Disease (Ceratocystis ulmi) usually kills most trees before they are 30 years old. Saplings are immune to the disease.

The trunk is distinct nearly to the top of the tree. The branches are often crooked and gnarled. The crown is broad and cylinder-shaped or somewhat oval.

The bark on young trees is dark reddish-gray and rough. On older trees it is dark gray and scaly with broad, flat-topped ridges and deep, irregular, interrupted furrows.

The twigs are light yellowish-brown and hairy, becoming hairless and dark reddish-brown or ash gray. In the second year branchlets develop 3 to 5 prominent, corky ridges.

The buds are reddish-brown, cone-shaped, sharply pointed, slightly hairy, and diverging from the twig.

The leaves are deciduous, alternate, and simple, and are attached to the twig on a 3 16 long leaf stalk. The blades are thick, oval to inversely egg-shaped, 2 to 4 long, and ¾ to 2 wide. They taper abruptly to a short, narrow point at the tip with concave sides along the tip. The base is asymmetrical, rounded on one side, tapering on the other. The upper surface is dark green, shiny, usually hairless, and smooth. The lower surface is paler green and somewhat hairy. The margins are doubly toothed from the tip to the base, the major teeth deeper and incurved. There are about 20 prominent veins on each side of the central axis. The veins are straight, end in a large tooth, and are rarely forked. In the fall the leaves turn bright yellow.

The flowers have both male and female parts. They are borne in racemes of 7 to 13 flowers on previous year’s twigs. They appear in early April to mid-May before the leaves. Individual flowers have no petals, 5 to 8 stamens with dark purple anthers, and greenish, hairy stigmas.

The fruit is a samara consisting of a dry, flattened, papery, oval, to in diameter wing surrounding a seed seed case containing 1 seed. It is hairy and has an additional fringe of hairs along the margin. The tip is pointed and shallowly notched. The wing is inflated and the seed case is not distinct from the wing.




40 to 60




The champion rock elm in Minnesota is on private property near Kandiyohi, in Kandiyohi County. In 2003 it was measured at 113 tall and 107 in circumference (34 in diameter), with a crown spread of 61.


Flower Color




Similar Species


American elm (Ulmus americana) trunk divides at the base of the crown. The branches are gracefully spreading. Older twigs are never corky. The buds are appressed to the twig, sharp pointed, and flattened. No more than 2 or 3 leaf veins are forked. Flowers and fruits are on long stalks. The samara is deeply notched and hairless except for a fringe of hairs along the margin. It is not inflated, and the seed case is distinct.

Slippery elm (Ulmus rubra) leaves have several forked veins. The upper leaf surface is hairy and very rough to the touch. The buds are blunt, not pointed, dark brown, and covered with conspicuous orange or reddish-brown hairs. The samara is round with a slightly notched tip and a line that extends from the base to the notch at the tip.


Rocky ridges, limestone bluffs. Full sun; moderately shade tolerant.




Early April to mid-May


Pests and Diseases






Distribution Map



2, 3, 4, 5, 7, 8, 28, 29, 30.









  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (flowering plants)  
  Superorder Rosanae  


Rosales (roses, elms, figs, and allies)  


Ulmaceae (elm)  


Ulmus (elms)  
  Subgenus Oreoptelea  
  Section Trichoptelea  

Subordinate Taxa





  Ulmus racemosa  

Common Names


cork elm

rock elm













A slim, cylindrical, drooping cluster of many flowers. The flowers have no petals and are either male or female but not both.



A corky, round or stripe-like, usually raised, pore-like opening in bark that allows for gas exchange.



An unbranched, elongated inflorescence with stalked flowers. The flowers mature from the bottom up.



A dry fruit consisting of a seed attached to a papery wing; one seeded in Elms and Ashes, two-seeded in Maples.


Simple leaf

A leaf that is not divided into leaflets, though it may be deeply lobed or cleft.

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Other Videos
  Trees with Don Leopold - rock elm

Published on Jun 27, 2012

No description available.

  Ulmus thomasii-Orme liè
Roger Latour

Published on Sep 29, 2012

Un spécimen de l'Orme liège (Ulmus thomasii, Orme à Thomas) sur un boulevard urbain à Montréal. L'arbre étant une espèce rare et protégée il est intéressant de le trouver ici en pleine ville.

A specimen of the cork elm (Ulmus thomasii Orme Thomas) on an urban boulevard in Montreal. The tree is a rare and protected species it is interesting to find it here in the city.






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