| 1 | Angle of lateral nerves with main nerve almost right, 80-90°.. |
| 1' | Angle of lateral nerves (basal nerves excepted), with main nerve much sharper, c. 30-60°, |
| 2 | Flower buds globose; stamens in bud and in young flower inwardly coiled, conspicuously protruding in anthesis; staminal appendages solid and clavate |
| 2' | Flower buds ovoid or ellipsoid; stamens in bud straight or sigmoid, in young flowers straight, not or slightly protruding in anthesis; staminal appendages inflated and petaloid |
| 3 | Filaments broad, tepal-like, at base 1.5-2.5 mm wide, the margins curved around the staminal appendages; interstaminal glands absent |
| 3' | Filaments narrow, not tepal-like, at base c. 0.5 mm wide, the margins not curved around the staminal appendages; interstaminal glands present. |
| 4 | Staminal appendages dorsally entire, not cleft |
| 4' | Staminal appendages dorsally cleft |
| 5 | Rim of staminal appendages conspicuously finger-like fringed, the fringes c. 0.5 mm long, inner perianth segments narrow, much narrower than outer perianth segments, c. 0.8 mm wide. Christmas I. (Indian Ocean) |
| 5' | Rim of staminal appendages with short fringes, c. 0.2 mm long; inner perianth segments about as wide as outer segments, c. 2 mm wide. Papua New Guinea |
| 6 | Fruit wings Ungulate, 3.5-6 cm long |
| 6' | Fruit wings hemi-orbicular, or sublingulate, 1.5-4 cm long |
| 7 | Staminal appendages pointed at the top, not curved; perianth segments c. 2 mm acuminate |
| 7' | Staminal appendages spathe-like, more or less hooded towards outside; perianth segments acute, or c. 0.5 mm acuminate |
| 8 | Flowers 10-12 mm long, subglabrous; leaves usually drying blackish-brown.. |
| 8' | Flowers 7-9 mm long, hairy; leaves drying brown |
