Illustration by Adelaide Tyrol
In her 1905 book, Our Native Trees and How to Identify Them: A Popular Study of Their Habits and Their Peculiarities, Harriet Keeler extols the unexpected qualities of the inner bark of slippery elm: “It is thick, fragrant, mucilaginous, demulcent, and nutritious. The water in which the bark has been soaked is a grateful drink for one suffering from affections of the throat and lungs.”
Keeler is neither the first nor the last to appreciate the inner bark of slippery elm. But before looking into its nutritional and medicinal qualities, note that the inner bark can be used to identify this species: if you find mucilaginous slime when chewing on a twig, it confirms that you’ve got a mouthful of Ulmus rubra.
Native Americans used the slippery bark of slippery elm to induce labor, as a wound dressing, to treat dysentery, coughs, and stomach problems, and for many other medical problems as well as for food, including flour. Early colonists were quick to copy them and added many other uses: it was used to treat pneumonia, consumption, skin ulcers, abscesses, and even leprosy. They, too, made nutritious flour out of dried elm bark, which, when mixed with milk, was given to invalids and infants. It is still a very common ingredient in herbal remedies.
It is no wonder that by 1875, George Emerson, the author of A Report of the Trees and Shrubs Growing Naturally in Massachusetts, feared for the tree’s survival because of excessive harvesting of the bark: “In many places I have found it dead or dying, from having been stripped of its bark…It is much to be regretted that the slippery elm has become so rare.”
The species did come back from over-harvesting, only to be hit by Dutch elm disease, beginning in the 1930s.
While not as susceptible to Dutch elm disease as American elm, slippery elm has always been less common in the Northeast, and the disease has had quite an effect: now, mature specimens that once reached 70 feet in height are hard to find. Like American elm, young trees are not killed by Dutch elm disease. The fungus is carried by bark beetles, and the bark of young trees is not thick enough to interest them. The tree grows from southwestern Maine west to the Dakotas, and as far south as central Texas and northern Florida. It’s most abundant in the southern parts of the Lake States and west throughout the corn belt.
Slippery elm thrives in the moist, rich soils that are found on riverbanks, wooded bottomlands, and flood plains. It can be found scattered in uplands if the soils are limey, but it’s never found in pure stands.
It takes a little care to distinguish this species from American elm, but it has distinctive features at all times of the year. In winter, the shape of a large tree will give it away: it is widespreading, often flat-topped, and the branches tend to be either horizontal or ascending, very unlike the familiar drooping habit of its best-known relative.
The buds, too, are distinctive: unlike American elm buds, they are covered with reddish-brown hairs, are dark in color, and are somewhat round. When young, the twigs are greenish and hairy, but they become gray and smooth. At any time of year, chewing on a twig will produce the gooey, slippery substance for which the tree is known.
The leaves of almost all the elms are simple and alternate, uneven at the base, and have doubly-toothed margins and straight veins that go right to the edge of the leaf. American elm leaves are smooth on the upper surface, but those of slippery are rough sandpapery (like 120 grit), and the lower surface is woolly (more like 220 grit). If you had both American and slippery elms leaves in your hand, you might notice that slippery ones are larger and darker green.
The short-stalked, purplish flowers appear in clusters, before the leaves unfurl, and the abundant pollen reaches its destination on the wind. The fruits, which ripen before the leaves have reached full size, are like little flat blister packs – a small seed encased in a papery wafer. Other elm seeds have hairy fringe on the wafer edges; slippery elm seeds are hairy all over the seed but hairless along the margins.
In the lumber business, slippery elm is called red elm, because of the color of the heartwood. Although considered somewhat inferior to American elm, both elm species have been used for boxes, crates, and barrels and are marketed together as “soft elm.”