Northern Prairie Wildlife Research Center
| Lead | Characteristic | Go To |
| 1 | Bracts subtending the flowers rounded on the back; corolla lobes 1 mm or more long; seeds 2-4 per capsule, 2-3 mm long. | P. eriopoda |
| 1 | Bracts subtending the flowers keeled on the back; corolla lobes less than 1 mm long; seeds 6-30 per capsule, 0.8-1.5 mm long. | P. major |