| 1 | Calyx subequally 5-toothed, not 2-lipped. |
| 1' | Calyx unequally 5-toothed, distinctly 2-lipped (the upper tooth generally larger and much broader than the others and forming the upper lip, and the others forming the lower lip). |
| 2 | Basic inflorescence a stalked cyme. Flowers small (calyx less than 2 mm, corolla 5-6 mm long); calyx teeth deltoid. |
| 2' | Basic inflorescence a verticillaster. Flowers proportionally large (calyx 4-4.5 mm, corolla 10-12 mm long); calyx teeth lanceolate. Corolla blue, prominently gibbous above. Aromatic. |
| 3 | Stamens long-exserted. Fruiting calyx 3.5-4 mm long. Corolla white, the tube gibbous above. Upper leaves sessile or even amplexicaulous |
| 3' | Stamens included in lower lip of corolla. Fruiting calyx 4.5-5 mm long. Corolla violet-blue, the tube not gibbous above. Upper leaves petioled |
| 4 | Median teeth and lower teeth similar in shape and length, free, and all with narrow, acute or acicularly acuminate apices. Inflorescence a verticillaster. |
| 4' | Median and lower teeth dissimilar in shape and length; median teeth shorter than the lower ones, with acute, rounded or truncate tip; lower teeth connate to various degree. |
| 5 | Flowering calyx (and entire inflorescence) densely covered with long greyish arachnoid pubescence, strongly declinate, the teeth all claw-like curved. Corolla tube shorter than the calyx. Inflorescence paniculate |
| 5' | Flowering calyx glabrescent or sparsely hairy, nearly straight, the teeth erect or reflexed, quite apart. Corolla tube longer than the calyx. Spurious spike solitary, or with 1 or 2 branches at the base, rarely paniculate (in P. apoensis and P. congest us). |
| 6 | Corolla tube curved and declinate or constricted near the median portion. Leaves orbicular or reniform in outline, more rarely ovate. |
| 6' | Corolla tube straight or bent near the base, neither strongly declinate nor constricted near the median portion. Leaves ovate or broadly ovate in outline. |
| 7 | Corolla tube not constricted in the middle, ± trumpet-like widened; filaments fused at the base into a tube around the style-base, exposed. Flowers 10-20 or more in a verticillaster |
| 7' | Corolla tube constricted near the median portion; filaments adnate to the throat of the corolla tube, enclosed. Flowers 6-8 in a verticillaster |
| 8 | Median and lower calyx teeth lanceolate, the median ones becoming broader and blunt in fruiting stage. Flowers numerous (usually over 20) in a verticillaster; inflorescence paniculate |
| 8' | Lower and median calyx teeth subulate, sharply pointed. Flowers less than 12 in a verticillaster; inflorescence a spurious spike, solitary or with 1 or 2 branches below. |
| 9 | Median teeth usually much shorter or less) than the lower ones, with rounded or truncate apices (rarely mucronate in 2 varieties of P. scutellarioides). |
| 9' | Median teeth slightly shorter (⅔ to ¾) than the lower ones, with acute or acuminate apices. |
| 10 | Fused 2 lower calyx teeth with an almost truncate apex with the dents wide apart. Roots with sessile tubers |
| 10' | Lower teeth deeply bifid at apex, but the teeth close, almost parallel. No tubers on roots. |
| 11 | Corolla c. 1 cm long (in some New Guinea specimens up to 18 mm), the tube with a curve, slender below the curve, rather suddenly widening above it. Flowers usually in verticillasters |
| 11' | Corolla c. 2 cm long, straight, the tube rather gradually widening, narrow funnel-shaped. Flowers in stalked cymes |
| 12 | Median teeth about 2./3 as long as the lower ones, in fruiting stage about half as long as the latter. In damp mossy forests above 1000 m. |
| 13 | Spurious spikes 2-4 cm long. Flowers 1-3 |
| 13' | Spurious spikes 5-25(-30?) cm long. Flowers 5-8(-l5) |
| 13'' | Median teeth about ¾ as long as the lower ones, in fruiting stage almost as long as the latter. On limestone hills in lowland below 200 m |
