|Populus deltoides - cottonwood|
|Populus heterophylla - swamp cottonwood|
The cottonwood is, variously, either a specific species of tree, Populus deltoides, or a section of the genus Populus that includes that species.
The cottonwood, Populus deltoides, is one of the larger North American hardwood trees, although the wood is rather soft. It is a riparian-zone tree.
Leaves are alternate and simple, with coarsely-toothed (crenate/serrate) edges, and subcordate at the base. Leaf shape is roughly triangular, hence the species name, deltoides. An important feature of the leaves is the stem which is flattened sideways, so that the leaves have a particular type of movement in the wind. Some other Populus species such as trembling aspen, Populus tremuloides, and bigtooth aspen, Populus grandidentata, share this characteristic. However, not all cottonwoods have this feature; for instance, the swamp cottonwood, Populus heterophylla, lacks it.
Male and female flowers are in separate catkins, appearing before the leaves in spring. The seeds are borne on cottony structures which allow them to be blown long distances in the air before settling to ground.
The cottonwood is exceptionally tolerant of flooding, erosion and filling around the trunk. It is also able to grow in moister areas on the Great Plains where most other trees cannot grow. A traveling salesman once planted a cottonwood seedling in the middle of one of the upper plains states, many miles from the next nearest tree, and watered it on his route every week. The tree survived and, once its roots were able to penetrate the water table, needed no further watering and lived for many years.