The poplar tree often goes by the name cottonwood; the name comes from the seeds of the tree, which develop in clusters of hanging capsules that ripen and open, scattering the white fluffy hairs with the seeds attached. The poplars in North America include the eastern cottonwood as well as the swamp cottonwood and species like the balsam poplar. Recognition of the poplars comes with identifying its special characteristics.
Judge the size of the poplars you encounter, focusing on overall height and the width of the trunk. Some eastern cottonwoods are massive. One in Ohio, according to the Ohio Public Library Information Network, grew to 139 feet tall with an 8-foot wide trunk. Not all poplars are this large, although most are at least medium-sized. The balsam poplar grows between 60 and 80 feet. Others, like black cottonwood, commonly grow to over 100 feet.
Observe the shape of a poplar from afar. A vase shape indicates species like the eastern cottonwood and the plains cottonwood, while others are upright with a narrow crown of limbs, such as the balsam poplar. An introduced ornamental from Europe, Lombardy poplar is a distinctly narrow tree shaped almost like a column of a building.
Examine poplar leaves carefully, paying attention to their size, colors and shapes. Most poplars native to the U.S. have leaves in the 4- to 6-inch-long range. The shapes will vary from one poplar type to the next. Some are oval or almost round (swamp cottonwood), but other have tapered ends and a triangular shape, like the foliage on a black cottonwood. Poplar leaves have serrations along their edges and the leaves are green, with the upper surface often darker than the lower. Many species' leaves change to yellow in the fall, before eventually flying off the limbs.
Study the reproductive process of the poplars to identify these trees. The poplars will have male and female flowers develop on separate trees, before the leaves emerge on the twigs. These flowers are catkins, compact drooping clusters of no ornamental importance, the University of Connecticut Plant Database says. Some are yellow while others may be brownish. The female cottonwood flowers turn into the hanging seed chains that will ripen and release the white tufts that fill the air in late June of July.