| 1 | Inflorescence a pedunculate umbel of 2 or more triads |
| 1' | Inflorescence other than a pedunculate umbel of triads (e.g., a head, simple umbel, solitary flower or sessile cluster) |
| 2 | Triads with all flowers closely sessile |
| 2' | Triads with at least the lateral flowers pedicellate |
| 3 | Rays in the umbel more than 10, arising from depressions in a globular dilation of the end of the peduncle |
| 3' | Rays in the umbel 3, arising at the end of an unthickened peduncle |
| 4 | Rays in the umbel 2-5 |
| 4' | Rays in the umbel 6-14 10 |
| 4'' | Rays in the umbel 15 or more 12 |
| 5 | Leaves opposite |
| 5' | Leaves with verticillate phyllotaxy, sometimes displaced to irregular spirals.. |
| 6 | Inflorescence axis more than 10 mm long; leaf lamina less than 10 cm long; petals free to the base |
| 6' | Inflorescence axis less than 10 mm long; leaf lamina more than 10 cm long; petals coherent at the base for 1-3 mm . |
| 7 | Inflorescence peduncle up to 10 mm long; petals 4 |
| 7' | Inflorescence peduncle more than 25 mm long; petals 5 or 6. |
| 8 | Leaves with opposite and decussate phyllotaxy, although sometimes displaced |
| 8' | Leaves with verticillate phyllotaxy, usually ternate or quaternate, sometimes up to 8-verticillate, sometimes displaced to irregular spirals |
| 9 | Inflorescence a pedunculate or sessile 6-flowered head formed from 2 sessile triads |
| 9' | Inflorescence not as above (a pedunculate or sessile simple umbel, a solitary flower or 3-flowered head) |
| 10 | Leaves sessile |
| 10' | Leaves obscurely or distinctly petiolate |
| 11 | Leaves truncate to cordate at the base; peduncle rudimentary (inflorescence sessile) . |
| 11' | Leaves cuneate to truncate at the base; peduncle 2-5.5 mm long. |
| 12 | Petals with deflexed spurs on the inside above the base forming a nectar chamber; bracts of the lateral flowers appressed to the ovary, not forming part of the involucre |
| 12' | Petals lacking deflexed spurs on the inside above the base; bracts of the lateral flowers spreading, forming part of the involucre |
| 13 | Inflorescence sessile; petiole broad, 1-3 mm long |
| 13' | Inflorescence peduncle 4-5 mm long; petiole slender, 5-15 mm long |
| 14 | Inflorescence a pedunculate capitulum formed from a single cymule of 3 sessileflowers |
| 14' | Inflorescence a simple umbel or solitary flower |
| 15 | Inflorescence a sessile 1- to 3-flowered umbel ( I.c., the flowers sometimes seemingly solitary); pedicels of the flowers mostly 1-4 mm long; corolla 5- or 6-merous |
| 15' | Inflorescence a pedunculate 2- to 4-flowered simple umbel; the peduncle 2-5 mm long; pedicels mostly 2-3 mm long; corolla mostly 4-merous |
| 16 | Inflorescence a 9-flowered head formed from 3 sessile triads, on a peduncle 12-15 mm long |
| 16' | Inflorescence not as above (a pedunculate or sessile simple umbel or a solitary flower) |
| 17 | Inflorescence a sessile 1- to 3-flowered umbel ( I.c., the flowers sometimes seemingly solitary) |
| 17' | Inflorescence a pedunculate simple umbel |
| 18 | Leaf lamina narrowly to broadly obovate, mostly rounded at the apex, mostly less than 10 cm long; pedicels of the flowers distinct, mostly 1-4 mm long; anthers on a short free filament |
| 18' | Leaf lamina ovate, shortly acuminate and obtuse at the apex, mostly more than 12 cm long; pedicels of the flowers very short or absent so that the inflorescence resembles a sessile cluster; anthers sessile |
| 19 | Umbel 2- to 4-flowered; peduncle 2-5 mm long; corolla mostly less than 20 mm long; leaves 2- to 4-verticillate |
| 19' | Umbel 4- to 6-flowered; peduncle 8-11 mm long; corolla more than 20 mm long; leaves 4- to 7-verticillate |
