Willow family (Salicaceae)
Description: This native deciduous tree is 60-120' tall at maturity. It develops a single stout trunk up to 4-6' across and forms an ovoid crown in open situations. The trunk bark of mature trees is thick, gray, and coarsely ridged. The abundant branches are ascending above and drooping below; they are somewhat crooked and knobby. Branch bark is light gray to gray-brown and fairly smooth. Alternate leaves are 4-5" long and 3-4" across; they are deltate-ovate in shape and crenate-dentate along their margins. The teeth of the leaves are slightly hooked. Individual leaves have flat bottoms and slender tips. The upper leaf surfaces are medium green and glabrous, while their lower surfaces are pale green, hairless, and dull. Leaf venation is pinnate. The slender petioles are nearly as long as the leaf blades; they are light green, glabrous, and somewhat flattened. Eastern Cottonwood is dioecious; individual trees produce either all male (staminate) flowers or all female (pistillate) flowers. These flowers are produced during the spring before the leaves develop in the form of drooping catkins about 2-3" long. Male catkins occur in clusters of 2-4 near the tips of branches, while female catkins are produced individually. Each male catkin is bright red or yellow and cylindrical in shape, consisting of a dense mass of nearly sessile male florets. Each male floret consists of a dish-shaped basal disk and 20-60 reddish or yellowish stamens. At the base of each male floret, there is a fringed bract. Each female catkin is green and cylindrical in shape, consisting of many female florets on slender petioles (see photo of Female Catkin). Each female floret consists of a dish-shaped basal disk and a single ovoid pistil about 8 mm. (1/3") long. Each pistil has 3-4 flattened stigmata with undulate margins. At the base of each female floret, there is a fringed bract. The florets are wind-pollinated. Afterwards, the male catkins wither away, while the female catkins elongate to 4-6" in length while developing their fruits. During early to mid-summer, these fruits split open to release their seeds. Each fruit releases about 30-50 seeds with cottony hairs. The seeds are distributed by the wind and can travel several hundred feet in the air. They also float on water and can travel downstream. Individual seeds are about 2 mm. long. The woody root system is shallow and branching. This tree reproduces by reseeding itself.
Cultivation: The preference is full sunlight, moist conditions, and soil consisting of sandy loam or silty loam. Growth and development of young trees is quite fast. However, mature trees are usually short-lived (100 years or less). Temporary flooding during the spring is tolerated. Because the wood of the branches is rather soft and brittle, this tree is vulnerable to storm and ice damage. For female trees, the cottony hairs of the seeds may be released in such numbers that they can clog gutters and the filters of air conditioners. Because the spreading roots wander in search of water, individual trees should not be planted near sewers or water pipes.
Range & Habitat: Eastern Cottonwood is a common tree that is probably found in every county of Illinois (see Distribution Map). Habitats consist of bottomland deciduous woodlands, banks of rivers and lakes, banks of mine spoil, picnic and camping grounds near sources of water, and sand dunes near Lake Michigan. Sometimes Eastern Cottonwood is cultivated as a landscape tree in yards. It frequently colonizes disturbed open areas that are moist. In bottomland woodlands, common associates are Black Willow, Green Ash, Slippery Elm, Silver Maple, and River Birch. There is a subspecies, Populus deltoides occidentalis (Western Cottonwood), that is found along rivers in the Great Plains region. It has smaller leaves with larger teeth than the typical eastern subspecies.
Faunal Associations: Eastern Cottonwood and similar species are an important food source of many insect species. The leaves are eaten by the caterpillars of the butterflies Limenitis archippus (Viceroy), Limenitis arthemis astyanax (Red-Spotted Purple), and Papilio glaucus (Tiger Swallowtail); they are also eaten by the caterpillars of the skipper Erynnis icelus (Dreamy Duskywing) and the caterpillars of many moth species (see Moth Table). Other insect feeders include many leaf beetles (see Leaf Beetle Table), larvae of long-horned beetles (see Long-Horned Beetle Table), larvae of the weevil Cryptorhynchus lapathi (Poplar-and-Willow Borer), aphids (see Aphid Table), plant bugs (Lopidea cuneata, Lygocoris hirticulus, & Tropidosteptes populi), the leafhopper Idiocerus lunaris, and larvae of the sawfly Trichiosoma triangulum. Many of these insects are important sources of food to insectivorous birds. Some birds feed on the buds and catkins during the spring when other sources of food are scarce; these species include the Ruffed Grouse, Prairie Chicken, and Purple Finch. Eastern Cottonwood provides nesting habitat for such birds as the Pileated Woodpecker (cavities in large trees), Baltimore Oriole, Warbling Vireo, Northern Parula, and Yellow Warbler (young trees). Some mammals also use Eastern Cottonwood as a food source. White-Tailed Deer browse on twigs and foliage of this tree, as does the Cottontail Rabbit when seedlings are within reach. Beavers use small trees as a source of food and also as construction material for their dens and dams. Like certain birds, tree squirrels sometimes eat the buds during the spring.
Photographic Location: Meadowbrook Park in Urbana, Illinois.
Comments: Eastern Cottonwood develops very quickly into a rather coarse and robust tree. Its shiny leaves glitter in the sunlight, and they make a conspicuous flapping sound in the wind that can be construed as either relaxing or annoying. This tree can be distinguished from its relatives from the deltate shape of its leaves, which have bottoms that are more or less flat. The narrowly rounded teeth of its leaves are somewhat unusual because they are slightly hooked, and it has flattened petioles, unlike some Populus spp. Trees that are referred to as 'poplars,' 'aspens,' and 'cottonwoods' are members of the same genus and closely related to each other.