| 1 | All leaves opposite. Hairs intra- and interpetiolar. |
| 1' | At least the middle-cauline leaves spirally arranged. Hairs if present only axillary. |
| 2 | The largest leaves obovate to spathulate. Axillary hairs inconspicuous. Sepals distinctly carinate (20 X magn.). |
| 2' | The largest leaves linear to elliptic (obovate to spathulate in P. macrorhiza from Timor). Hairs mostly conspicuous. Sepals not carinate (20 x magn.), occasionally with an apical, dorsal, about dome-shaped hood. |
| 3 | Mostly 1-3 involucral leaves with an axillary axis. Capituli (2-)3-30-flowered. Stamens 7-15. Fruit c. 4 mm long. |
| 3' | Involucral leaves mostly without axillary axes. Capituli (1-)2-3(-6)-flowered. Stamens 18-50. Fruit c. 7 mm long. |
| 4 | Largest leaves obovate to spathulate, c. 8 mm wide. Timor. |
| 4' | Largest leaves linear to elliptic, less than 4 mm wide. Pantropic. |
