| 1 | Corolla lobes without a long thin terminal tail, < 15 mm long |
| 1' | Corolla lobes drawn out into long thin tails, > 20 mm long |
| 2 | Leaves with 8-16 pairs of secondary veins which are straight and form an angle of 70-90° with the midrib; corolla lobes 5-10 mm long; anther acumen 4-4.3 mm long |
| 2' | Leaves with 5-9 pairs of secondary veins which are curved and form an angle of 45-65° with the midrib; corolla lobes 4-8.5 mm long; anther acumen 1.8-2 mm long |
| 3 | Corolla puberulous outside; anther acumen 5.5-7.5 mm long. — Lesser Sunda Islands |
| 3' | Corolla glabrous outside or puberulous only at top of tube and lobes; anther acumen 7.5-19 mm long |
| 4 | Corolla tube 9.5-19 mm long; anthers 10-16 mm long; leaves normally papery when dry, 2-12.6 cm long |
| 4' | Corolla tube 13-32 mm long; anthers 13-25 mm long; leaves papery or coriaceous when dry, (5-)8-23 cm long |
