Some species of poplar trees are commonly called cottonwoods. There are different species of poplar growing throughout the United States. You can identify poplar trees by recognizing certain features. A field guide to trees of North America is also an aid in identifying different types of poplars.
Use the range maps in your field guide to determine which poplars are native to your part of the country. The eastern cottonwood, for example, can be found across much of the eastern half of the nation. By knowing which types of poplar tree are in your area, you can concentrate your efforts on those species. In many places in the United States there is just a single type of poplar tree. In California you will find the Fremont cottonwood and no others. In terms of where to look to find a poplar, you should first check areas such as river and stream banks. Poplars prefer moist soil and thrive along waterways.
Recognizing the leaves of a poplar tree is the best way to identify the species. Search for a tree with leaves shaped like spades from a deck of cards. The leaves are toothed and a rich green on top in summer. The color on the bottom of the leaf will be paler than above. The leaves will flutter in even the slightest of breezes. The shape of the leaf and the length of its stem make this happen. You may actually hear a poplar tree before you see it when the wind is blowing.
There is a reason some poplars are called cottonwoods. This can help you to identify the tree. In the late spring and early summer the seedpods of a poplar will burst open. These pods, which are tiny, green and shaped almost like a flask, contain strands that closely resemble cotton. The seeds are attached to a fluffy bit of this cotton-like tuft and are scattered throughout the countryside when the wind blows.
The wood of a poplar tree is very soft in comparison to the wood of most other trees. In the spring the twigs have elongated and pointy buds. There will be overlappiong scales on them, and they grow off the twig at angles. The typical poplar will have smooth bark as it matures, but once it has grown, the bark will be fissured and ridged. Some poplar species, like the eastern cottonwood, are renowned for having extremely thick bark.