| 1 | Stems succulent, armed; leaves usually absent |
| 1' | Stems not succulent, usually unarmed (if armed, then leaves present); leaves present |
| 2 | Carpels 1-several, distinct, ovule 1 per carpel, or carpels 2 or more, united in a compound ovary with as many locules and ovules as carpels |
| 2' | Carpels always 2 or more, united in a compound ovary, ovules more than 1 per carpel |
| 3 | Leaves alternate; inflorescence not subtended by a involucre; tepals free, not petaloid |
| 3' | Leaves often opposite; inflorescence often subtended by a conspicuous involucre; perianth connate in a petaloid tube simulating a corolla |
| 4 | Leaves succulent; ovary superior or inferior |
| 4' | Leaves usually not succulent; ovary superior |
| 5 | Perianth with only tepals, not petaloid |
| 5' | Perianth with sepals and petals, or sepaloid bracteoles and tepals |
| 6 | Perianth greenish, herbaceous; filaments free |
| 6' | Perianth scarious, dry; filaments connate below in a tube |
| 7 | Sepals or sepaloid bracteoles 2 |
| 7' | Sepals 4 or 5 |
| 8 | Herbs or subshrubs; ovules 2-several; fruit a capsule |
| 8' | Vines; ovule 1; fruit indehiscent |
| 9 | Leaves alternate, opposite or whorled; petals absent or inconspicuous; ovary with 2-several locules |
| 9' | Leaves opposite; petals usually present, conspicuous; ovary with 1 locule |
