The slippery elm tree has a range very similar to the American elm, growing in the eastern United States from Canada south to northwestern parts of Florida. It exists westward to Texas in the South and North Dakota in the North. Slippery elm has many different traits, which you can look for when trying to identify one.
Inspect the size and the shape of a slippery elm tree. This species has a somewhat flattened upper crown with spreading branches. The trunk on a mature slippery elm can be as wide as 2-1/2 feet and the tree rarely grows taller than 70 feet.
Look for an uneven base where it attaches to the stem. The leaves of slippery elm are oblong and 4 to 6 inches long, according to the Virginia Department of Forestry website. They have serrated edges and are dark green on the top side but much paler below. Feel the underside of the leaf and you will notice that it is coarse. In the autumn, the leaves may change from green to yellow, but most stay some shade of green.
Watch for the flowers on a slippery elm to appear in very early spring, even before the tree's leaves open up. They grow in clusters of between threes and fives. These flowers are a light shade of green and are small.
Search a slippery elm in the spring for its samaras, a term that describes a paper-like seed case. These samaras are green, round and smooth except for where the seed exists in the center, which is brownish and fuzzy. They resemble an inch wide egg-over-easy, but with green and brown where the white and yellow colors would be.
Chew the twigs of slippery elm and you will notice they are sticky. The inner bark is moist, a feature that gives the tree its odd name. Native-Americans and settlers would steep the inner bark in water to treat sore throats and coughing. The University of Maryland Medical Center website says this is because slippery elm contains a substance known as mucilage, which when mixed with water creates a sort of thickened gel.
Inspect a cross-section of slippery elm wood and you will see that the inner bark feels slippery and that the inner wood is a reddish-brown color. The innermost bark has a slight aroma and the "National Audubon Field Guide to Trees" says it is edible.