| 1 | Inflorescence thyrsoid |
| 1' | Inflorescence a loose or congested panicle |
| 2 | Head of corolla in bud narrower than tube; corolla lobes < 0.6 times as long as tube |
| 2' | Head of corolla in bud as wide as or wider than tube, if narrower only slightly so and then flat-topped; corolla lobes > 0.7 times tube length |
| 3 | Head of corolla bud wider than tube, rounded; stamens included or exserted in mature flower. — Eastern Malesia |
| 3' | Head of corolla bud not noticeably wider than tube, ± flat-topped; stamens included. — Western Malesia |
| 4 | Corolla lobes ≤ 0.6 times as long as tube; corolla bud head mostly narrower than tube |
| 4' | Corolla lobes > 0.6 by tube length; corolla bud head mostly as wide as or wider than tube, sometimes narrower |
| 5 | Inflorescence pubescent; corolla tube > 2 mm long |
| 5' | Inflorescence glabrous; corolla tube ≤ 2 mm long |
| 6 | Head of corolla bud wider than tube, rounded; stamens included or exserted in mature flower |
| 6' | Head of corolla bud not noticeably wider than tube; stamens included |
| 7 | Corolla tube glabrous outside |
| 7' | Corolla tube pubescent outside |
| 8 | Young branchlets puberulent; corolla tube > 2 mm long |
| 8' | Young branchlets glabrous; corolla tube ≤ 2 mm long |
| 9 | Corolla tube 5.7-6.6 mm long |
| 9' | Corolla tube 1.4-4 mm long |
| 10 | Inflorescence a loose panicle, not robust; bracts deciduous |
| 10' | Inflorescence congested, robust; bracts usually persistent |
