with petiole=___ flat  or  petiole=◯ round :

Petiole=___ flat

blade base=___ flat, ▴▴▴▴ teeth=very small (>5/cm) (>12/in), tree very tall thin
🇪🇺 ◼︎ European black poplar  Populus nigra

blade base=___ flat, ▲▲ teeth=medium (2-3/cm) (5-8/in)
eastern cottonwood  Populus deltoides

blade base= rounded (U-shaped), ▲▲ teeth=few+large, leaf longer than wide
bigtooth aspen  Populus grandidentata

blade base= rounded (U-shaped), ▴▴▴▴ teeth=small, leaf about as long as wide
quaking aspen  Populus tremuloides

Learn more about aspen/​cottonwood/​poplar genus Populus

Part of willow  family Salicaceae.

Uses by native peoples
(Ethnobotany database)

Populus hosts caterpillars of 367 species
of butterflies and moths, in some areas.
  This plant is also known to be a host for (in areas where invasive) 🐝︎ spotted lanternfly (SLF)  Lycorma delicatula.

Often grows in clonal colonies [1] —look around for other stems!

🔍︎ 🔍︎ images Discover Life Encyclopedia of Life Michigan Flora Minnesota Wildflowers Flora of North America NRCS PLANTS db USFS Wikipedia