| 1 | Corolla hairy |
| 1' | Corolla glabrous. |
| 2 | Midrib prominent on the upper surface |
| 2' | Midrib impressed in the upper surface. |
| 3 | Twigs hairy. |
| 4 | Leaves distichous |
| 4' | Leaves spirally arranged. |
| 5 | Underside of leaves glabrous. (If leaf margin and petiole beset with closely spaced vesicular glands: 3. S. adenophylla.) |
| 5' | Underside of leaves hairy. |
| 6 | Upper side of leaves hairy (pulverulent) |
| 6' | Upper side of leaves glabrous. |
| 7 | Ovary glabrous, calyx longer than 1 mm. Bracts longer than 1 mm |
| 7' | Ovary hairy. |
| 8 | Leaf index more than 3. Leaf margin (and petiole) beset with closely spaced glands. Ovary 1-2 mm high |
| 8' | Leaf index 2-3. Leaf margin (and petiole) often glandular but glands not closely spaced. Ovary c. 1 mm high |
| 8'' | Twigs glabrous. |
| 9 | Calyx and/or ovary hairy. |
| 9' | Calyx and ovary glabrous. |
| 10 | Ovary hairy. Inflorescence a raceme. Calyx glabrous |
| 10' | Ovary glabrous. Inflorescence a spike. Calyx hairy. |
| 11 | Inflorescence axis glabrous. |
| 11' | Inflorescence axis hairy. |
| 12 | Petiole less than 20 mm |
| 12' | Petiole more than 20 mm. |
| 13 | Nerves less than 10 pairs |
| 13' | Nerves more than 10 pairs. |
| 14 | Angle of leaf base 25-40°. Inflorescence a (basally branched) spike, forming a cone in bud. |
| 14' | Angle of leaf base more than 60°. Inflorescence a raceme |
