Populus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar /ˈpɒp.lər/, aspen, and cottonwood.In the September 2006 issue of Science Magazine, the Joint Genome Institute announced that the Western Balsam Poplar (P. trichocarpa) was the first tree whose full DNA code had been determined by DNA sequencing.