| 1 | Leaves radical, long-petioled, palmately nerved. |
| 1' | Leaves not radical, sessile or shortly petioled, pinnately nerved. |
| 2 | At least the lower (submersed) leaves pinnately divided, verticillate. |
| 2' | All leaves entire to crenate-serrate, opposite, alternate or sometimes in whorls of 3-4. |
| 3 | Fruit breaking up into 2-4 mericarps. Leaves sessile. |
| 3' | Fruit a one-seeded nutlet. Leaves mostly shortly petioled. |
| 4 | Flowers in axillary clusters, the middle one ♂, or sometimes ☿ and (in Asiatic spp.) very long-stalked, the other ones ♀. |
| 4' | Flowers solitary, all ☿, not long-stalked. |
