| 1 | Stamens free, not united into a ligule; petals not clawed, ovary uni- or bilocular. |
| 1' | Stamens united into a strap-shaped ligule; the 2 anterior petals unguiculate and enveloping the ligule in buds; ovary unilocular |
| 2 | Ovary unilocular, inserted at or near base of receptacle. |
| 2' | Ovary bilocular, inserted at mouth or midway up receptacle. |
| 3 | Inflorescence a panicle of cymules; fertile stamens 7-26. |
| 3' | Inflorescence racemose; fertile stamens 2 or 5 |
| 4 | Stamens 15-26, the filaments hairy, exserted |
| 4' | Stamens 7-10, the filaments glabrous, included |
| 5 | Fertile stamens 6-8(-9), markedly unilateral, the filaments equal or not exceeding the calyx lobes. |
| 5' | Fertile stamens 10-50, usually inserted around complete circle; the filaments far exserted beyond calyx lobes. |
| 6 | Lower leaf surface glabrous or lanate, with stomatal cavities; bracteoles not enclosing small groups of flowers; inflorescence a panicle of cymules; ovary inserted midway up receptacle |
| 6' | Lower leaf surface usually areolate with stomatal cavities; bracteoles enclosing small groups of flowers; inflorescence a much-branched panicle; ovary inserted at mouth of receptacle |
| 7 | Stamens 10-25; inflorescence little branched panicles, or racemes |
| 7' | Stamens c. 45; inflorescence much-branched corymbose panicles |
