The Plains Cottonwood is a large native deciduous tree forming a tall trunk, up to 100 feet high and diameters often larger than 4 feet. The crown is open and spreading with slightly drooping stout branches. The largest known specimen in Minnesota (2020) is in Chippewa County - height 106 feet, crown spread 110 feet, circumference 394 inches.
The bark is smooth when young, light gray to yellow-green, turning gray with age becoming very thick, rough, and deeply furrowed.
Twigs are very stout, brownish, with slight angles. The buds are large, about 3/4 inch long and covered with several green-brown resinous scales. Over-wintering buds have fine hair. A crushed twig has a bitter aspirin taste.
Leaves are triangular, 3 to 7 inches long and 3 to 5 inches wide, alternate, simple, with long pointed tips and straight to heart-shaped bases and curved (slightly hooked) coarse teeth on the margin. They are shiny green on top, pale green under, and have a long slender, flattened stalk which has 2 round glands on the top side. The leaf tapers to a long pointed tip. Fall color is a brilliant yellow.
As with most trees, all leaves will be slightly variable in shape and size on the same tree. P. deltoides is strongly heterophyllous, that is, it has two types of leaves - those that are formed in the winter bud for early spring growth, known as preformed or early leaves and leaves produced later in the season known as neoformed leaves. The later leaves will be different in size and number of teeth and are the last to fall from the tree in Autumn.
Flowers: Cottonwood is dioecious, that is male and female flowers occur on separate trees. Flowers are in 2 to 3 inch drooping catkins. Male catkins (staminate) are in clusters of 2 to 4 at the branch tips. The color is red to yellow and each small flower on the catkin has a saucer shape basal disk with 30 to 40 stamens. Female catkins (pistillate) appear singly or in opposite pairs, are green and the individual small flowers are stalked. They have a basal disk, a 4 chambered ovary and pistil with 2 to 4 flattened stigmata. Both male and female catkins have (+ or -) 15 to 40 individual flowers. The catkin stalks are of uniform length. Flowers appear before the leaves and are wind pollinated. Catkins are also called 'aments'.
Seed: After pollination, the female catkins elongate up to 6 inches in length and the fertilized flowers produce an elliptical seed capsule, green initially, turning brown. Then the capsule splits and releases 7 to 10 seeds per ovary chamber; the seeds are attached to white cotton-like hair and are dispersed far and wide by the wind in early summer. Trees need to be about 10 to 15 years of age to produce seed. Seed germinates immediately.
Habitat: Plains Cottonwood in its native habitat is found in moist bottomlands. It will tolerate a wide range of soils as long as they are well-drained. Trees require full sun and are generally shade intolerant. The root system is wide and branching and deeply penetrating to find moisture. This tree should not be planted near wells and underground water pipes. Plains Cottonwood does not sucker; it can re-sprout from a stump but not vigorously but is a vigorous self-seeder.
Names: The genus Populus is the Latin name for the Poplar. The species, deltoides, is from the Greek letter 'Delta' and refers to the delta shape of the leaf. The author names for the plant classification are as follows: First to publish was ‘Bartram’ which refers to John Bartram (1699-1777) early American botanist and explorer who traveled extensively in the colonies collecting plants. He sent many plants to Europe, including many to Linnaeus who considered him the ‘greatest natural botanist is the world'. In 1765 he became “The King’s Botanist” for North America. His work was not complete and was amended by ‘Marshall’ which refers to Humphry Marshall (1722-1801), American Botanist, who published in 1785 - Arboretum Americanum: The American Grove, an Alphabetical Catalogue of Forest Trees and Shrubs, Natives of the American United States.
Comparisons: There are three subspecies of this tree that somewhat overlap geographically. The subspecies recognized as the native to Minnesota is subsp. monilifera, which is called the Plains Cottonwood. There is another subspecies, subsp. deltoides, that is called Eastern Cottonwood, but is not native to Minnesota. It has leaf tips that are very short pointed, either 0 or 3 to 6 leaf stalk glands, winter buds without hair, and the catkin stalks are longer and not of uniform length. The third subspecies, subsp. wislizeni or Rio Grande Cottonwood, is native to 7 states of the southern Rocky Mountains. It has 0 leaf glands and winter buds with hair.
Above: Various tree shapes of Cottonwood. The example in the 1st photo has multiple trunks branching close to the base and is squeezed around a shorter Black Willow on the right side. The tree in the 2nd & 3rd photos, has a single trunk. Both show the open crown.
Below: 1st photo - is the typical rough and deeply furrowed bark of cottonwood trunks, - 2nd photo - frequently the trough of the furrow is lighter color.
Below: 1st photo - the upper branches which have smoother gray-ish white bark. 2nd photo - twigs have slight angles and green-brown resinous buds.
Below: 1st photo - Plains Cottonwood leaves have long pointed tips and straight to heart-shaped bases, curved (slightly hooked) coarse teeth on the margin and a slender flattened stalk that has 2 glands at the base. 2nd photo - For a comparison, this is the very similar looking leaf of the Rio Grande Cottonwood, P. deltoides subsp. wislizeni
Male Catkins: Below 1st photo - the catkin prior to elongation. 2nd photo - in the early spring, in process of elongation.
Below: Female aments starting to elongate.
Male Catkins: Below- 1st photo - partially elongated catkin; 2nd photo - the male flowers just emerging; 3rd photo - The male flowers fully developed with the stamens on filaments from the basal disc of the flower.
Below: 1st photo - The fertile female catkins develop a number of green 4-chambered seed capsules, each of which can have 28 to 40 seeds. 2nd photo - The female seed capsules splitting to release seeds to the wind.
Below: A leaf comparison of the four Minnesota native species of Populus plus the introduced P. alba. Images not to scale.
Below: The brilliant fall color of a Rio Grande Cottonwood, P. deltoides subsp. wislizeni. Photo Nov. 10, 2017 near the Rio Grande River at Bernado NM.
Notes: Plains Cottonwood is considered indigenous to the Garden area and Susan Wilkins added some young plants in 2011 to enhance the tree canopy in the woodland area. The subspecies monilifera is found in North America in the Great Plains region and somewhat eastward, but not into the southern states where the dominant subspecies is subsp. deltoides. This is why the common name of Plains Cottonwood is preferred. In Canada the range is from British Columbia east to Ontario. In the U.S. the range is from the Rocky Mountain states of Montana south to New Mexico eastward as far as Texas and Oklahoma and then up to Missouri, Illinois and Wisconsin. There are reports of stands in several states further east but this range excludes the southern states and New England. Within Minnesota, it is found in most counties with a few scattered exceptions, mostly absent in the NE section.
There are only four species of Populus that are native and commonly found in Minnesota: P. balsamifera, Balsam Poplar; P. deltoides, Plains Cottonwood; P. grandidentata, Bigtooth Aspen; and P. tremuloides, Quaking Aspen. Two others are reported: One is a native cross - P. X jackii, Jack's Cottonwood, which is usually sterile [The DNR does not track county populations of it]; and the other is the introduced P. alba, White Poplar.
Uses: Cottonwood wood is light, soft and weak but has a uniform texture so it is used in plywood, paper pulp, and lumber for uses not requiring bending or compression strength.
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"