| | 1. Leaf blade white-tomentose below |
| P. alba |
| | 1' Leaf blade glabrous or hairy below |
| |
| P. angustifolia |
| | 2' Leaf blade ovate, nearly round, or triangular |
| |
| | 3. Leaf blade triangular, margin coarsely scalloped |
| P. fremontii subsp. fremontii |
| | 3' Leaf blade ovate to nearly round, margin finely scalloped |
| |
| | 4. Leaf blade narrowly to widely ovate, 3–7 cm; petiole 1/3–1/2 blade length, round in X-section |
| P. balsamifera subsp. trichocarpa |
| | 4' Leaf blade widely ovate to nearly round, generally 2–4 cm, petiole 2/3 to = blade length, laterally compressed in X-section |
| P. tremuloides
|