Elm trees are a familiar sight in many landscapes, known for their large canopies and stately presence. Identifying these trees by their unique leaf and bark characteristics offers a deeper connection with the natural world.
Distinctive Leaf Characteristics
Elm leaves display several features that aid in their identification. A primary characteristic is their asymmetrical base, meaning one side of the leaf blade extends further down the petiole (leaf stalk) than the other. This unevenness is a consistent trait across many elm species.
Another distinguishing feature is the double-serrated margin, where smaller teeth appear on larger teeth, giving the leaf edge a finely toothed appearance. Elm leaves are oval or elliptical with a pointed tip, and their surfaces can vary from smooth to rough, often feeling like sandpaper due to fine hairs. Prominent venation, with veins running straight to the leaf margins, is common, and leaves are arranged alternately along the twigs.
Unique Bark and Tree Form
The bark of mature elm trees provides clear identification clues. It appears deeply furrowed, with interlacing ridges that can form patterns resembling diamonds or rectangles. The color ranges from gray to dark brown, with some species exhibiting reddish-brown hues.
Beyond the bark, the overall growth habit of an elm tree is recognizable. Many elm species develop a distinctive “vase-like” or “umbrella-like” shape, with branches arching upwards and outwards from the trunk. Younger elm twigs exhibit a zig-zag pattern, where each bud and subsequent leaf is slightly offset, creating a noticeable change in direction along the stem.
Comparing Common Elm Varieties
Several elm species are commonly encountered, each with subtle differentiating features. The American Elm (Ulmus americana) is known for its classic vase shape and large leaves, which are 3 to 5 inches long and have a sandpapery feel on the upper surface. Its bark shows alternating layers of reddish-brown and cream or buff-colored tissue when viewed in cross-section.
Siberian Elm (Ulmus pumila)
The Siberian Elm (Ulmus pumila), sometimes called “dwarf elm” due to its smaller stature, has smaller leaves, 1 to 2 inches long. These leaves are elliptic and can be less asymmetrical at the base than American Elm leaves. Its bark is dark gray with irregular longitudinal patterns, and its twigs have a delicate, wispy appearance.
Slippery Elm (Ulmus rubra)
Slippery Elm (Ulmus rubra), also known as Red Elm, has larger leaves than American Elm, 4 to 7 inches long, and they are notably rough or abrasive on both upper and lower surfaces. The inner bark of the Slippery Elm is mucilaginous, giving it a slick or slippery feel when chewed, which is a unique identifier.
Differentiating Elms from Look-Alikes
Several other trees can be mistaken for elms due to similar leaf or bark characteristics. The Hackberry (Celtis occidentalis) is a common look-alike, as it also has asymmetrical, toothed leaves and a somewhat vase-like form. However, Hackberry bark is distinctly warty or knobby, with cork-like protuberances, unlike the more furrowed bark of elms.
Basswood (Tilia americana)
Basswood, also known as American Linden (Tilia americana), can be confused with elm. Basswood leaves are heart-shaped and have serrated margins, but they are more symmetrical at the base than elm leaves. The bark of Basswood is flat with long, running lines, and it can have sprouts originating from the base of the tree.
Beech (Fagus grandifolia)
Beech trees (Fagus grandifolia) have smooth, gray bark, a distinct contrast to the furrowed bark of elms. While Beech leaves are also serrated, they are smoother and thinner than elm leaves, lacking the rough texture of elm species.