| 1 | Epicarp crustaceous-verrucose; mesocarp thick, hard, fibrous; endocarp breaking up irregularly on germination; cotyledons at least slightly ruminate. |
| 1' | Epicarp smooth and glabrous or distinctly lenticellate but not crustaceous; if lenticellate then endocarp opening by a pair of basal stoppers to allow seedling escape. Cotyledons not ruminate. |
| 2 | Stamens free to base (can often be seen persistent around base of young fruit). Cotyledons ruminate |
| 2' | Stamens united into a unilateral ligule. Cotyledons only slightly ruminate |
| 3 | Epicarp lenticellate; opening by a pair of basal stoppers to allow seedling escape, always thick and woody; fruit bilocular, but often only one loculus developing seed |
| 3' | Epicarp glabrous and smooth without lenticels; opening by lateral plates, longitudinal lines or no special mechanism of seedling escape; fruit uni- or bilocular. |
| 4 | Endocarp opening by a pair of lateral plates to allow seedling to escape; endocarp thick and woody or thin and bony. |
| 4' | Endocarp not opening by lateral plates, usually opening longitudinally; endocarp thin and bony. |
| 5 | Fruit unilocular; endocarp very thin, bony |
| 5' | Fruit bilocular; endocarp thick, woody |
| 6 | Fruit usually bilocular, 1.5-5 cm long, sometimes sagittate with a distinct stipe, not ridged 4. Hunga b. Fruit unilocular, either 1-1.3 cm long, ellipsoid or 2-5 cm long and ridged. |
| 7 | Fruit ridged. Leaves orbicular |
| 7' | Fruit smooth, not ridged. Leaves oblong to elliptic |
