P. alba: tree; leaves deciduous, cordate-ovate, angularly toothed, snow-white and densely downy beneath ; catkins sessile, about two inches long. - White Poplar or Abele. The Grey Poplar is a variety with smaller leaves. - Damp woods. Fl. March.
P. tremula: tree; leaves deciduous, orbicular or rhom-boidal, smooth on both sides, irregularly and rather coarsely toothed, with slender stalks which twist readily, so as to keep the leaves in motion; catkins small. - Aspen. - Woods. Fl. March, April.
P. nigra: tree; leaves deciduous, triangular-ovate, tapering at the point, serrated, smooth on both sides; catkins two inches long, lax, cylindrical. - Damp places. Fl. March.