American Elm is a large native long-lived deciduous tree, sometimes developing forking trunks with a broad rounded to vase-like crown composed of many spreading branches drooping at the ends. Trunk bases frequently have buttresses. Trees grow to 100+ feet with a diameter of 4 feet.
The bark is light gray, spongy when young, becoming a darker gray with age and developing deep furrows that fork into flat-topped diamond shaped ridges. Old growth branches will be smooth.
Twigs are brownish, slender, slightly zigzag, without hair in the fall and then can be covered with fine hair in the spring. Buds are ovate, reddish brown with darker scale edges (which edges may have fine hair) and with the laterals often placed somewhat to one side of the twig above a leaf scar. Flower buds are smaller and all lateral. The leaf buds are larger and the terminal bud is always a leaf bud.
Leaves are in 2 rows, alternate, simple, thin, elliptical 3 to 6 inches long and 1 to 3 inches wide with a short stalk. The margins are double-saw-toothed, the bases are rounded with unequal sides. Tips are pointed, the lateral veins are parallel with several lateral veins near the base showing forks, the upper surface is dark green and slightly rough (nature's sandpaper) while the underside is paler and usually with fine hair. There will be variability in leaf shape and size. There are a pair of linear narrow stipules at the base of the leaf which dry up and fall away early. Fall color is yellow.
Flowers in the genus Ulmus are bisexual. They appear clustered along the twigs in small drooping clusters of 3 to 5 in early spring before the leaves. Each flower is only 1/8 inch across on a 1/2 inch stalk, with a reddish-green calyx of 7 to 9 shallow lobes with hairy margins, 7 to 9 stamens with red anthers and a single white deeply divided style. The stalks elongate after pollination. They are cross pollinated by the wind.
Seed: The fertile flowers form a flattened elliptical single seeded samara, about 3/8 to 1/2 inch long. These are brown at maturity and the papery wing of the samara is hairy on the edges. It hangs from the same elongated stalk as the flower. The tip of the samara has a notch with the points of the notch curving inward. These mature rapidly in late spring to early summer and are dispersed by the wind. They can germinate immediately. Seeds may be produced as early as 15 years of tree age, but 40 years is more normal.
Habitat: American Elm likes full sun, fertile soil, but many soil types, and moist to mesic conditions. The root system is shallow and spreading but in dry soils a tap root will develop. It reproduces from seed and stump sprouts. Unfortunately the tree is susceptible to the Dutch Elm disease which has decimated local populations, including those in the Garden. See below. It was noted by Thomas Nuttall as far back as the early 19th Century that “the Elm is subject to many diseases, and attacked by many kinds of insects."
Names: The genus Ulmus, is the Latin word for Elm. the species name, americana, means 'of America'. The author name for the plant classification, 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: The most confusing comparison is with U. rubra, the Red or Slippery Elm. There the leaves are similar, but the winter buds have more hair, not just on the scale edges, the flowers are not stalked, and the samaras of the seeds do not have hairy edges. The The Siberian Elm, U. pumila, likewise has samaras without hairy edges, but the flower buds are round, with reddish-black scales, the flowers in a tight fascicle without stalks, similar to U. rubra, but the leaves have a mostly symmetrical base with a single saw-toothed margin and are much smaller, only up to 1 inch wide.
Above: Bark of this young tree is beginning to develop the deep fissures typical of Elm bark. Leaves (2nd photo) are elliptical, with short stalks and unequal bases. The margins (3rd photo) are double-saw-toothed and the lower lateral veins fork at the margin.
Below: The underside of the leaf (2nd photo) is paler and usually with fine hair, and clearly demonstrates the parallel vein pattern. There is a pair of linear narrow stipules at the base of the leaf that fall away early. (1st photo).
Below: Twigs and buds: A fall twig (1st photo) shows little hair on the surface whereas in spring (2nd photo) the twig is hairy. Lateral buds are positioned above a leaf scar. The terminal bud in the fall (3rd photo) shows the reddish-brown scales with darker edges and some surface hair.
Below: Flowers are in small drooping clusters of 3 to 5 in early spring before the leaves. 1st photo - flower bud just breaking open. 2nd photo - full development.
Below: Seed formation: Flowers (1st photo) and green seeds form before the leaves emerge. The newly formed green seeds (2nd photo) already have the fine edge hair that is characteristic of American Elm. The brown mature seeds (3rd photo)
Below: 2nd photo - Mature seeds are formed as the leaves emerge. Note the notch at the tip with the notch tips pointing inward.
Thoreau wrote in Wild Fruits: "Before the 10th of May, the winged seeds or samarae of the elms give them a leafy appearance, or as if covered with little hops, before the leaf buds are opened. This must be the earliest of our trees and shrubs to go to seed. It is so early that most mistake the fruit before it falls for leaves, and we owe to it the first deepening of the shadows in our streets."
Notes: American Elm was indigenous to the Garden. Eloise Butler catalogued it (as White Elm) on April 29, 1907. It is widespread in the eastern half of North American, as far west as Montana and Colorado in the US and Saskatchewan in Canada. In Minnesota, native populations were found throughout the state with only scattered exceptions.
Dutch Elm Disease: This disease, imported from Europe in the 1930s, has wiped out the Garden's extensive population of American Elm. Gardener Ken Avery's first notation in his reports about the disease occurs in his Report for 1964 to the Board of Park Commissioners, dated March 12, 1965, when he mentions that he had the help of a tree trimming crew to remove dead and dying elm wood. He then states that he believed he made an important finding as to the sanitation of diseased wood. He found that it took only one fourth of time to debark a tree as it did to cut it up. Because there were so many large large elms in the bog area of the Garden and just outside the Garden, removal would be difficult and this might be an important remedy to control the disease. [Note: it has been established by arborists that removing the bark from dead elm wood was sufficient to prevent the spread of the disease, so Ken’s remedy was on the mark.]
The progress of the disease was to last for many years. In 1975 Ken noted that the Park Board was removing diseased elms from the swamp area behind the Garden and that three trees had been removed within the Garden in 1974. In 1976 half of the remaining elms in the Garden died during the summer. Friends president Alexander Dean also noted that the loss of tree canopy in the Woodland Garden, causing the growth of brush, vines and heavy weeds, would require re-planting of trees. Beginning in the fall of 1977, small trees were being planted to replace elm losses This process continued for years during Ken's tenure as Gardener. The scourge began in 1963 and by 1986 94,988 trees had been removed with 105,012 remaining - all within the City of Minneapolis. Most of those in the Garden were lost by that time although there would be further removals of elm into the 1990s.
Uses: The wood of American Elm is coarse, heavy, but strong. It warps and splits badly and is thus used only for small wood products. Francois Michaux noted that in the 18th and early 19th Centuries the wood was used for the naves (hubs) of coach-wheels at New York and further north where it was difficult to procure the desired Black Gum. Its main use was as a ornamental, particularly as a boulevard tree. The inner bark was also used by Native Americans for medicinal purposes.
As an ornamental, the White Elm was prized and was exported to Europe where Thomas Nuttall said "In France the Elm is subjected to being trimmed in artificial forms, flat surfaces, and for hedges; it is very patient of the knife."
It is easy to see why, with its height and shape, the tree was used so much as a boulevard tree, forming arches over the avenues. Francois Michaux wrote "In clearing the primitive forests a few stocks are sometimes left standing; insulated in this manner, it appears in all its majesty, towering to the height of 80 or 100 feet, with a trunk 4 or 5 feet in diameter, regularly shaped, naked and insensibly diminishing to the height of 60 or 70 feet, where it divides into two or three primary limbs. The limbs, not widely divergent near the base, approach and cross each other 8 or 10 feet higher, and diffuse on all sides long, flexible, pendulous branches, bending into regular arches and floating lightly in the the air."
Quotes from Michaux and Nuttall are from Volume 3 of "North American Sylva". (Ref. #26D)
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"