Trees & Shrubs of the Eloise Butler Wildflower Garden

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 ‘W.Bartram’ refers to William Bartram (1739-1823) early American botanist, ornithologist and naturalist, son of naturalist John Bartram. He traveled extensively in the colonies in search of new plants and bird, was the first to do so in Florida and published Bartram’s Travels, which was read extensively and like his father’s writings, had an influence on the school of Romantic writers in England, especially Coleridge and Wordsworth. 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.