| 1 | Leaves opposite |
| 1' | Leaves in whorls of 3 or more |
| 2 | Leaf blade ratio 10.7-20 times as long as wide, leaf blade linear, flowers solitary |
| 2' | Leaf blade ratio 1.6-8.8 times as long as wide, leaf blade not linear, if narrow then sides not parallel; flowers in cymes |
| 3 | Leaves pubescent above and beneath |
| 3' | Leaf pubescence variable but not pubesent all over above |
| 4 | Flowers solitary or an inflorescence of only 2 flowers |
| 4' | Flowers in cymes with 3 or more flowers |
| 5 | Bracteoles several along pedicel; pedicels 1-3 mm long; sepal apices obtuse, 2.3- 2.8 mm long, sparsely to densely puberulent |
| 5' | Bracteoles 2 immediately beneath calyx; pedicels c. 6 mm long; sepal apices acuminate, c. 1.8 mm long, sepals glabrous |
| 6 | Corolla tube < 4 mm long — Palawan |
| 6' | Corolla tube > 4 mm long. — Throughout the Philippines |
| 7 | Bracteoles present on the pedicels of all flowers. — Throughout the Philippines |
| 7' | Bracteoles absent or only on the pedicel of the terminal flower in an inflorescence. — Palawan |
| 8 | Many bracteoles on pedicels; inflorescence densely puberulent; 39-55 pairs of secondary veins |
| 8' | 1 or 2 bracteoles on pedicels, very rarely more but then inflorescence at most sparsely pubescent and secondary veins < 39 pairs |
| 9 | Corolla lobe apex acuminate; leaves reaching 2.5-7 cm long, often notched at the apex even if acuminate; ovary pubescent all over |
| 9' | Corolla lobe apex rounded to acute, very rarely to acuminate but then leaves > 10 cm long, not notched; ovary glabrous, pubescent around base only or pubescent all over |
| 10 | Inflorescence with more than 1 whorl of flowers and clear internodes, not robust; fruit usually with several globose articles |
| 10' | Inflorescence with only 1 whorl of flowers at the end of the peduncle, rarely with more but then internodes short, inflorescence robust and fruit with 1 or 2 ellipsoid articles |
| 11 | Corolla tube continuously pubescent except for base inside; leaves to 20 cm long. — Not in Palawan or Sulu |
| 11' | Corolla glabrous or pubescent in upper half only inside; leaves < 10 cm long (in the Philippines). — Palawan, Sulu |
| 12 | Leaves thickly coriaceous, often somewhat fleshy, margin weakly to strongly inrolled; corolla slightly fleshy |
| 12' | Leaves papery to coriaceous, not fleshy, margin flat or weakly inrolled; corolla not fleshy |
