American Elm / Florida Elm

Think American elm, Ulmus americana and visions of a beautifully landscaped, tree-lined walkway might come to mind. Or a shady urban park. Traditionally, it’s been among the most popular, maybe even beloved, landscaping trees in Canada and the eastern United States.

Then three dreaded words: Dutch elm disease.

The fungal infection has devastated elm tree populations, especially in landscapes where the trees have been planted in rows or groves close together to the exclusion or near-exclusion of other species.

You might think of the elm as a tree of the Northeast, but it’s native to the U.S. and Canada as far west as Saskatchewan, Montana and Wyoming. The elm's natural range also includes the Sunshine State as far south as Collier and Palm Beach counties. Florida even has its own elm tree, Ulmus american variety floridana, aka the Florida elm. Some have classified the Florida elm as a species unto itself, Ulmus floridana, but that hasn’t been accepted as valid by the greater scientific community. (It's not totally clear that even the subspecies is fully accepted.)

The Florida elm is extremely rare in South Florida — the Institute for Regional Conservation considers it to be critically imperiled here — but it can be found growing in the wild at a few conservation sites, including the Allapattah Flats Wildlife Management Area in Martin County. It’s also present at the Green Cay Nature Center in Palm Beach County. Elms also can be used here as a landscaping tree, though it does have its drawbacks. More on that later.

One bit of good news: as of this writing (August 2023), Dutch elm disease has yet to be detected in Florida’s elm population. Arborists, however, remain vigilant for any sign of the disease.

Overall, whether the elm tree is vulnerable to extinction is a matter of opinion. The International Union for Conservation of Nature considers the elm to be endangered, while the equally authoritative website, NatureServe Explorer, gives the elm an “apparently secure” rating. The difference apparently has to do with how the two organizations weigh different data. NatureServe does list elms as imperiled in Wyoming and vulnerable in West Virginia and Maryland. On the other hand, it has it as secure in five states — Iowa, Illinois, New York, North Carolina, Pennsylvania and Virginia, plus Ontario in Canada.

For what it’s worth, NatureServe has no ranking for Florida’s elm population.

Elms are tall trees, typically 60 to 80 feet high, capable of hitting 200 feet in dense forests, with a spread between 50 and 70 feet wide. The shape of the tree is commonly described as like a vase, wide at the top and quickly tapering. It usually has a single, straight trunk with light brown to gray bark that becomes fissured and flakey. The trunk can divide into two "codominant" trunks; when it does, the joint becomes a weak spot susceptable to splitting.

The Florida Elm is a little smaller but similar otherwise.

The leaves are oblong, dark green and described as being double serrated along the outer edges. Look at the leaves and you’ll see prominent serrations; look closer and you’ll smaller serrations on the serrations. They are simple and arranged alternately along the stem.

Elm trees produce small, green flowers in clusters that develop at the leaf axils, the point where a leaf stem, or petiole, meets the branch that bears it. Bloom time in most of the elm’s range is the spring, as early as January in Florida. The flowers give way to a flat, thin seed pod that’s a favorite food of birds and other small animals. Elms are wind-pollinated.

Elms take to full sun or partial shade. They prefer moist habitats, including alluvial woods, swamp forests and deciduous woodlands.

Elms are larval hosts for the comma, question mark and painted lady butterflies.

According to the Native American Ethnobotany website, more than a dozen tribes from the Mid-Atlantic states to the Rocky Mountains used elms for everything from food — the Cheyenne made a coffee-like drink from the inner bark — to medicine, preparing treatments for colds, coughs, dysentery, broken bones, tumors, appendicitis, menstrual problems, aid in childbirth and a whole lot more. Elms provided building material, from shingles (the Chippewa) to support beams and posts; the wood was used to make tools and toys, saddles, dogsled harnesses (the Iroquois) and canoes. It’s still used to make furniture and veneers.

Its graceful looks make it a candidate as a landscaping tree even in South Florida. But as we noted earlier, it does have its share of drawbacks. For one — and a very big one — branches are susceptable to breakage under strong winds. Mature elms can produce tons of seeds that scatter everywhere and can be a chore to clean up. And being wind pollinated, elms can be a problem for those of us who are prone to allergies.

Dutch elm disease, which despite the name, likely orginated in Asia, was introduced to the United States as well as parts of Europe in the 1920s and 1930s, according to the Morton Arboretum. Dutch pathologists did some of the early work studying the disease, and the association with the Netherlands stuck for some reason..

It is a fungal disease carried by several species of bark beetle. Females will lay their eggs in the bark of infected trees; when adult beetles emerge, they fly off carrying fungal spores with them, infecting new trees as they eat their leaves. From there, the spores get into the trees’ vascular system; the trees respond by producing chemicals that plug up the system, causing the tree to wilt and eventually die.

Dutch elm disease has killed literally hundreds of thousands of elm trees in the 90 years or so that it has been in North America. The good news is that infected trees can be treated if the disease is caught early. There are also resistant cultivars available.

Other common names for American elm include white elm, water elm and soft elm. Elms are members of Ulmaceae, a family that includes various elms and other related tree species.

Blue Spring State Park