Northern Prairie Wildlife Research Center
| Lead | Characteristic | Go To |
| 1 | Staminodes 3-parted; sepals with a narrow hyaline margin. | P. glauca |
| 1 | Staminodes (5)7- to many-parted; sepals herbaceous throughout. | Lead 2 |
| 2 | Leaf blades ovate to subrotund, broadly rounded to usually cordate at the base, not decurrent on the petiole; bract-leaf often clasping; petals 7- to 11-nerved. | P. palustris |
| 2 | Leaf blades elliptic to elliptic-ovate, tapered to and decurrent on the petiole; bract-leaf not clasping; petals usually 5(7)-nerved. | P. parviflora |