| 1 | Leaves verticillate |
| 1' | Leaves not verticillate. |
| 2 | Midrib prominent in the upper surface. |
| 2' | Midrib impressed on the upper surface. |
| 3 | Twigs glabrous. Petiole more than 5 mm |
| 3' | Twigs hairy. Petiole 1-5 mm |
| 4 | Corolla hairy (in the Philippines sometimes nearly glabrous!) |
| 4' | Corolla glabrous. |
| 5 | Twigs hairy. |
| 5' | Twigs glabrous. |
| 6 | Leaves distichous |
| 6' | Leaves spirally arranged. |
| 7 | Calyx divided into three 2½ mm long lobes |
| 7' | Calyx not so. |
| 8 | Leaves crowded towards the end of the twigs. Twigs thick, tapering towards the apex. Fruits 3-celled. Apex of leaves rounded or acute |
| 8' | Leaves evenly distributed. |
| 9 | Underside of leaves glabrous. (If leaf margin and petiole beset with closely spaced vesicular glands: 3. S. adenophylla). |
| 9' | Underside of leaves hairy. |
| 10 | Ovary hairy, c. 1 ½ mm high. Inflorescence a lax raceme. Bracts to c. 1 mm long. Calyx lobes c. ½ mm long. Stamens c. 25 |
| 10' | Ovary glabrous (hidden between bracts!). Inflorescence a spike. |
| 11 | Upper side of leaves hairy (pulverulent) |
| 11' | Upper side of leaves glabrous. |
| 12 | Ovary glabrous. |
| 12' | Ovary hairy. |
| 13 | Leaves longer than 10 cm. Petiole more than 5 mm. Nerves more than 10 pairs. Calyx lobes longer than 1½ mm. Stamens more than 30. Disk glabrous. Style base glabrous. Fruits ampulliform |
| 13' | Leaves shorter than c. 10 cm. Petiole 1-5 mm. Nerves 4-11 pairs. Calyx lobes ½-1½ mm long. Stamens 15-40. Disk hairy. Style base hairy. Fruits not ampulliform |
| 14 | Leaf margin (and petiole) beset with closely spaced glands. |
| 14' | Leaf margin (and petiole) often glandular but glands not closely spaced. |
| 15 | Style base glabrous. |
| 15' | Style base hairy. |
| 16 | Bracts to c. 1 mm long. Calyx lobes c. ½ mm long, not triangular. |
| 16' | Bracts 2-3 mm. Calyx lobes 1-1½ mm, triangular |
| 17 | Intramarginal vein present. Inflorescence a fascicle. Fruits ampulliform |
| 17' | Intramarginal vein absent. Inflorescence a (basally branched) spike. Fruits ellipsoid to orbicular |
| 18 | Calyx and ovary glabrous. |
| 18' | Calyx and/or ovary hairy. |
| 19 | Inflorescence a (basally branched) spike. |
| 19' | Inflorescence not a spike. |
| 20 | Acumen longer than 5 mm |
| 20' | Acumen shorter than 5 mm. |
| 21 | Angle of leaf base less than 60°. Bracts 2-3 mm. Calyx lobes c. 2 mm long. Style base hairy. |
| 21' | Angle of leaf base c. 90°. Bracts 3-5 mm. Calyx lobes longer than 2½ mm. Disk glabrous. |
| 22 | Bracts and bracteoles persistent. |
| 22' | Bracts and bracteoles caducous. |
| 23 | Leaves 2-5¾ cm. Inflorescence a (basally branched) raceme. Bracts longer than 3 mm. Calyx regularly 5-lobed, calyx lobes semi-ovate. Fruits ovoid, 5-7 mm long, 1-celled. |
| 23' | Leaves 7½-H cm. Inflorescence a fascicle. Bracts 2-3 mm long. Calyx 3-lobed, the lobes semi-elliptic. Fruits ellipsoid, 11 mm long, 3-celled |
| 24 | Inflorescence axis glabrous. Corolla 3-4 mm. Calyx lobes not becoming longer by tearing. |
| 24' | Inflorescence axis hairy. Corolla 4-6 mm |
| 25 | Inflorescence a spike. Ovary glabrous. |
| 25' | Inflorescence a (sometimes compound) raceme. Ovary hairy. |
| 26 | Ovary ½-l mm high |
| 26' | Ovary 2½ mm high |
| 27 | Inflorescence a very lax raceme of 4-10 cm. Pedicels slender, 2-15 mm. Axis of raceme sparsely pulverulent-puberulous. Stamens c. 25 |
| 27' | These characters not combined |
