| 1 | All leaves opposite. |
| 1' | All leaves alternate or some of the leaves opposite. |
| 2 | Inflorescences branched. |
| 2' | Inflorescences unbranched and sessile. |
| 3 | Herbs. |
| 3' | Treelets, shrubs or subshrubs. |
| 4 | Pistillate flower with a perianth. |
| 4' | Pistillate flowers without perianth. |
