Northern Prairie Wildlife Research Center
| Lead | Characteristic | Go To |
| 1 | Pistils or achenes in a single whorl on a flat receptacle, mostly fewer than 20. | Genus Alisma |
| 1 | Pistils or achenes numerous and crowded in a dense cluster on a globose receptacle. | Lead 2 |
| 2 | Flowers mostly imperfect, with the male above the female in the inflorescence; achenes laterally flattened and winged; leaves usually sagittate. | Genus Sagittaria |
| 2 | Flowers all perfect; achenes turgid, strongly ribbed; leaves never sagittate. | Genus Echinodorus |