Slippery elm (Ulmus rubra), also called red elm, is a native elm of the eastern and central United States. It looks a lot like American elm from a distance, so people often walk past it without noticing. Up close it is one of the easier elms to recognize, because several of its features are rough and fuzzy where American elm’s are smooth.
The short answer: run your hand over the top of a leaf. Slippery elm leaves are 4 to 8 inches long, lopsided at the base, doubly toothed and very rough, like sandpaper, on top, with soft hairs underneath. The twigs are downy and the winter buds are covered in rusty red hairs. Its seeds are round, flat, papery wafers with a hairy center. The inner bark is slick, which gives the tree its name.
Where slippery elm grows
Purdue University notes that slippery elm grows across much of the eastern and central United States, from Minnesota south into central Texas, west to central Kansas and Nebraska, and along the east coast from northern Florida to Vermont. It is often found in upland woods, while American elm tends to grow in moist valleys and river bottoms. The Morton Arboretum lists it as tolerant of a wide range of conditions, including clay, alkaline soil, dry sites and wet sites.
The Morton Arboretum describes it as a large, fast-growing tree, 40 to 60 feet tall and 30 to 50 feet wide, with a vase shape.
Leaves: the sandpaper test
The leaves are the best feature from late spring to fall.
- Size: the Morton Arboretum gives 4 to 6 inches; Purdue Arboretum gives 4 to 8 inches by 2 to 4 inches wide. Either way, they are generally larger than American elm leaves.
- Shape: simple and alternate, with a long, tapering point and a very lopsided (oblique) base, one side of the blade starting lower on the stalk than the other.
- Edge: doubly serrated, meaning large teeth with smaller teeth on them.
- Texture: Purdue Arboretum describes the upper surface as very rough and the underside as covered in dense hairs. Vanderbilt’s elm key uses this “sandpaper” feel above as a main way to separate slippery elm from American elm.
- Color: dark green in summer, dull yellow in fall.
American elm leaves can also be slightly rough, so judge them together with the twigs and buds.
Twigs and buds: the winter clues
Slippery elm is easy to identify in winter if you look closely at the twigs.
- Twigs: downy and rough, with many raised lenticels, according to Purdue Arboretum. Vanderbilt’s key describes slippery elm twigs as scabrous (sandpaper-like).
- Buds: covered in a rusty red fuzz. American elm buds are generally smooth and glossy.
Those fuzzy, reddish buds are one of the most reliable features you can find.
Bark: ridges and a slick inner layer
The Morton Arboretum describes the bark as gray, ridged and furrowed, and Purdue University notes its strong vertical ridges. Bark alone is not a reliable way to separate slippery elm from American elm, so use it together with the leaves, twigs and buds.
The inner bark is moist and slippery, which is where the common name comes from. Please do not cut into a living tree to check; it opens a wound. A fallen branch will show you the same thing.
Flowers and seeds
Small, inconspicuous red-green flowers appear in early spring before the leaves. The fruit, a samara, follows in spring. The Morton Arboretum describes it as a seed surrounded by a circular, wafer-like wing. Purdue Arboretum notes the reddish-brown hairs over the seed in the center. American elm samaras are similar in size but have a fringe of hairs on the edge of the wing, so a hairy center with a smooth wing points to slippery elm.
Slippery elm vs. other elms
| Feature | Slippery elm | American elm | Siberian elm |
|---|---|---|---|
| Leaf size | 4 to 8 in | Usually smaller | 1 to 3 in |
| Leaf base | Very lopsided | Lopsided | Nearly equal |
| Leaf top | Very rough, sandpapery | Often smooth | Not sandpapery |
| Buds | Fuzzy, rusty red | Generally smooth, glossy | Small |
| Seed | Round, hairy center only | Hairy fringe on the wing | Small, winged |
| Native? | Yes | Yes | No, introduced |
Descriptions from Purdue Arboretum, Vanderbilt’s elm key and the Morton Arboretum.
Siberian elm is a non-native tree. The Morton Arboretum describes its leaves as only 1 to 3 inches long and fairly equal at the base compared with other elms. If the leaves are small and nearly symmetrical, you are probably looking at Siberian elm.
Dutch elm disease and slippery elm
The Morton Arboretum notes that slippery elm is susceptible to Dutch elm disease and does not recommend planting it in the Chicago region. Purdue Arboretum notes it is less severely affected than American elm, but it is still vulnerable. The Arboretum explains that the disease is carried by elm bark beetles and can also pass through root grafts between nearby elms.
The classic sign is “flagging”: leaves on a branch wilt, turn yellow and finally brown. Brown streaks in the wood under the bark of affected branches are further evidence, though only a lab test confirms the disease. If you see this on an elm, contact a certified arborist quickly, because early action gives nearby elms the best chance.
A quick checklist
- Is the leaf lopsided at the base and doubly toothed? You have an elm.
- Does the top feel like sandpaper? Points to slippery elm.
- Are the twigs downy and the buds rusty red and fuzzy? Slippery elm.
- Is the seed round with a hairy center and no fringe? Slippery elm.
- Are the leaves small, 1 to 3 inches, with a nearly even base? Probably Siberian elm.
For help with other trees, visit the tree identification hub, or compare pale-barked trees in birch vs. aspen.
Sources
- Slippery Elm, The Morton Arboretum
- Ulmus rubra (Slippery Elm), Purdue Arboretum Explorer
- Intro to Trees of Indiana: Slippery Elm, Purdue University Forestry and Natural Resources
- Elm Illustrated Key, Vanderbilt University Bioimages
- American Elm, The Morton Arboretum
- Dutch Elm Disease, The Morton Arboretum
Top photo: Famartin, CC BY-SA 4.0, via Wikimedia Commons