| 1 | Leaves subverticillate, in a terminal whorl or clustered at intervals. Inflorescences cauliflorous and/or axillary. Petals valvate. |
| 1' | Leaves spaced, spiral. Inflorescences often terminal, and/or axillary, rarely also cauliflorous. Petals imbricate (except in S. aruensis). |
| 2 | Unbranched shrub-like treelet or slender tree. Papillae distinct on the lower leaf surface. Lateral branches of the inflorescences usually at right angles with the main axis. |
| 2' | Branched shrub or tree. Papillae indistinct or obscure on the lower leaf surface. Lateral branches of the inflorescences obliquely ascending |
| 3 | Petals glabrous outside. Leaves (26-)40-52(-100) by 12½-17(-24) cm; apex obtuse or rounded |
| 3' | Petals hairy (puberulous or sericeous) outside. |
| 4 | Papillae indistinct on the lower leaf surface. Lateral branches of inflorescences ± perpendicular to the main axis |
| 4' | Papillae distinct on the lower leaf surface. Lateral branches of inflorescences obliquely ascending. |
| 5 | Papillae on the lower leaf surface separated into small groups by veins and veinlets |
| 5' | Papillae on the lower leaf surface not like above, but rather uniform. |
| 6 | Petals valvate |
| 6' | Petals imbricate. |
| 7 | Petals with 15-20 longitudinal veins |
| 7' | Petals with c. 4-c. 12 longitudinal veins. |
| 8 | Petals sericeous outside. |
| 8' | Petals puberulous outside. |
| 9 | Leaves with 15-32 pairs of nerves; apex rounded or slightly apiculate; veins much elevated beneath. Petals with c. 4 longitudinal veins |
| 9' | Leaf with 10-15 pairs of nerves; apex abruptly acuminate-rostrate; veins distinct beneath. Petals with c. 7 longitudinal veins |
| 10 | Leaves 5-8(-18)cm long; nerves 5-10 pairs; veins reticulate. ♀ Flower sessile, after falling leaving a short stalk 3-5 mm long |
| 10' | Leaves larger, 10-48 cm long; nerves 9-26 pairs; veins reticulate-scalariform, or reticulate and some cross-bar-like. ♀ Flower pedicelled (1-3 mm), after falling not leaving a short stalk. |
| 11 | Leaf apex obtuse, sometimes slightly apiculate |
| 11' | Leaf apex acute or acuminate, sometimes obtuse, rarely slightly emarginate. |
| 12 | Leaves 15-22 cm long. Petals with c. 12 longitudinal veins |
| 12' | Leaves larger, (23½-)35-48 cm long. Petals with c. 8 longitudinal veins |
