The group of trees with the scientific name of Populus belongs to the Willow family and includes poplars and aspens. Cottonwood is an alternate name for poplars because of the method in which the tree's seeds disperse on the wind, buoyed by a white tuft of hair. Different varieties of the poplars exist in North America, with some covering huge sections of the continent.
The balsam poplar grows farther north than any other North American hardwood species, states BorealForest.org, with this species among the few trees that can grow close to the Arctic Circle. Balsam poplar also ranges from one side of the continent to the other, distributed from Alaska eastward to Labrador and as far south as Minnesota, Michigan and Maine. The tree takes its name from its resinous buds, which possess a strong scent of balsam. This species can grow to 100 feet high and often exists in large stands of trees. Balsam poplar features a straight trunk with few branches and a shallow root system that leaves the tree vulnerable to high winds. The leaves are from 3 to 5 inches long and up to 3 inches wide, with a broad shape that tapers to a pointed tip. Balsam poplar is an important tree in much of Canada, used for making boxes, crates and paper.
White poplar and black poplar are introduced species of poplars that are native trees in Europe. The two poplars are significant landscaping trees in the United States, with white poplar growing to 100 feet tall and black poplar up to 60 feet. Black poplar has a column shape, while white poplar is a tree with a spreading crown. White poplar has bark that is whitish and both trees have leaves that change to yellow in the autumn. Both of these poplars require full sun and moist soil to thrive. Cultivars of the white poplar include the Globosa, a dwarf type, and the Richardii, another smaller version that is a slow-growing poplar. Black poplar hybrids include the Majestic, bred to resist disease.
The Plains cottonwood grows on the eastern side of America's continental divide and is the tallest broadleaf tree in many parts of its range. The Plains cottonwood stands out on the prairie and can sometimes attain massive sizes, with heights over 100 feet and trunks as wide as 7 feet. The species is short-lived, like all poplars, with few living much longer than 100 years. Plains cottonwood releases its cottony seeds from the early part of June into the middle of July, with the wind sending the seeds everywhere. The leaves of Plains cottonwood are triangular and between 3 and 6 inches long. The stems are sometimes as long as the leaves and serve to allow the foliage to rustle in the breeze. Plains cottonwood is prone to rotting, which results in the wind snapping off large branches.