| 1 | Papillae on the lower leaf surface indistinct or obscure. Petals valvate |
| 1' | Papillae on the lower leaf surface usually distinct. Petals imbricate (at least at the apex in S. prainii). |
| 2 | Papillae usually surrounding the endings of veinlets and arranged in groups. 18. S. lucens b. Papillae not as above, rather evenly arranged. |
| 3 | Leaves pubescent or velutinous on the lower surface. |
| 3' | Leaves glabrous, or sometimes sparsely puberulous on the lower surface. |
| 4 | Leaf apex obtuse, sometimes slightly emarginate, or acute. Petals with c. 8 longitudinal veins. Hypocarp obconical, stalk-like |
| 4' | Leaf apex shortly and abruptly acuminate. Veins of petals invisible. Hypocarp short-cupular or discoid |
| 5 | Petals only imbricate at the apex. Hypocarp obconical, stalk-like. Leaf veins reticulate |
| 5' | Petals imbricate. Hypocarp discoid. Leaf veins reticulate, or some cross-bar-like and subparallel. |
| 6 | Flower after falling leaving a short stalk of ½-3 mm. (Exine of pollen grains reticulate) |
| 6' | Flower after falling leaving no distinct stalk. (Exine of pollen grain striate) |
