Cottonwood (the genus Populus) is composed of 35 species which contain the aspens and poplars. Species in this group are native to Eurasia/north Africa [25], Central America [2] and North America [8]. All species look alike microscopically. The word populus is the classical Latin name for the poplar tree. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.