Identifying Local Elm Trees
While the American Elm tree was devastated by the "Dutch" Elm Disease, there are other species of Elm trees, both native and invasive, growing around Acton.
Elm trees all have one leaf per node (alternate), and simple leaves with toothed edges. The base of the leaf is cordate (heart-shaped), and asymmetric. (If the base is symmetric, you are probably looking at a Birch tree)
The different Elms are confusingly similar. They are listed here starting with the ones most commonly found in Acton.
Slippery Elm
The Slippery Elm (Ulmus rubra) is probably the most common native Elm in Acton at this time. It is a smaller tree (usually no more than 50 ft. tall), frequently competing with birches in wet areas.
Slippery Elm is chiefly distinguished from American elm by its downy twigs, chestnut brown or reddish hairy buds, and slimy red inner bark. The lateral veins in a Slippery Elm leaf typically fork before reaching the edge of the leaf, versus the American Elm having lateral veins which rarely fork.
Slippery Elm has small hairs along the edges of the leaves (marginal cilia), which differentiates it from Scotch Elm and English Elm.
Unfortunately, it apparently readily hybridizes with the invasive Siberian Elm.
Siberian Elm
The Siberian Elm (Ulmus pumila) is an invasive species frequently found along road edges in Acton.
In general it has smaller, more evenly sized leaves, and straighter stems/branches. The definitive tell is that the leaf edges have medium-sized to coarse teeth, whereas other Elms have leaf edges with teeth, with smaller teeth on them.
American Elm
The American Elm (Ulmus americana) was the largest species of Elm, commonly more than 100 ft. tall. It was largely wiped out by the introduction of the "Dutch" Elm Disease (DED), beginning in the 1930s. In 2023, there is no knowledge of old American Elms in Acton.
There has been work on identifying and breeding varieties with adequate resistance to DED. An Acton citizen has been working since 1994 to re-introduce these resistant variants back into Acton's conservation lands. Some of these are now approaching 30 years of age and 40 ft. in height.
Rock Elm
The Rock Elm (Ulmus thomasii) is a native Elm found in the midwest, into the western edge of Vermont and NH. No sightings in Massachusetts.
It has branches which are irregularly winged with 2 or more corky plates.
Scotch Elm
The Scotch or Witch Elm (Ulmus glabra) is closely related to the Slippery Elm, but reaches taller heights (100 ft). It is native to the British Isles, and found throughout Europe. It might also be found in yards around Acton as an ornamental tree.
Slippery Elm has small hairs along the edges of the leaves (marginal cilia) and the winter bud scales are red, versus no hairs along leaf edges in Scotch Elm, which has reddish-brown or brown winter bud scales.
Chinese Elm
The Chinese Elm (Ulmus parvifolia) is included in this list as it has been planted by towns in the area, and may be found in yards around Acton.
It has a very distinctive smooth peeling bark which sets it apart from the other Elm species.
English Elm
The English Elm (Ulmus minor 'Atinia') is another European Elm which might be found in a yard, or escaped from it. It is a sterile clone, regenerated by root suckers, and given its susceptibility to DED, GoBotany's reporting of it's presence in NE is suspect.
It has branches which are irregularly winged with 2 or more corky plates, similar to Rock Elm.