Key to the species of South American clade of Lobelia sect. Rhynchopetalum

1. Corolla shorter than 2.8 cm long, unilabiate, in shades of white or greenish ...................................................................................2.

– Corolla longer than 3 cm long, sub-bilabiate, frequently in shades of purple or pink ......................................................................3.

2. Stem and leaves glabrescent; bracts deflexed; seeds winged, wing in equal size to the seminiferous nucleus ................................... ................................................................................................................................................................................... Lobelia exaltata

– Stem and leaves densely tomentose; bracts erect; seeds not or slightly winged, wing when present narrower than the seminiferous nucleus....................................................................................................................................................................... Lobelia hassleri

3. Leaf blade ovate to suborbicular, margin crenulate to serrate; bracts ovate to suborbicular; seeds not winged.................................. ........................................................................................................................................................................... Lobelia santos-limae

– Leaf blade linear, lanceolate or oblong, margin entire, denticulate or dentate; bracts linear to lanceolate; seeds winged ...............4.

4. Leaves, bracts and fruits pubescents or puberulous ..........................................................................................................................5.

– Leaves, bracts and fruits glabrous .....................................................................................................................................................7.

5. Leaf blade tomentose on both surfaces; seeds slightly winged, wing narrower than the seminiferous nucleus.................................. .............................................................................................................................................................................. Lobelia thapsoidea

– Leaf blade tomentose only on the abaxial surface; seeds pronouncedly winged, wing equal size to the seminiferous nucleus ......... ...........................................................................................................................................................................................................6.

6. Stem glabrous; leaves with yellowish tomentum, leaf margin entire to denticulate, unhardened teeth; hypanthium campanulate .... .............................................................................................................................................................................. Lobelia brasiliensis

– Stem pubescent; leaves with whitish tomentum, leaf margin dentate, hardened teeth; hypanthium semi-globose............................. .............................................................................................................................................................................. Lobelia organensis

7. Leaf margin double serrate, teeth longer than 1 mm long; secondary veins arranged in 31–38 pairs ................ Lobelia glazioviana

– Leaf margin denticulate to dentate, teeth shorter than 0.5 mm long; secondary veins arranged in 9–27 pairs.................................8.

8. Bracts conspicuous, erect, frequently covering the pedicels; wing of seeds wider than the seminiferous nucleus ............................. .................................................................................................................................................................................. Lobelia fistulosa

– Bracts inconspicuous, deflexed, not covering the pedicels; wing of seeds narrower than the seminiferous nucleus.......................9.

9. Latex yellowish; inflorescence congest; bracteoles up to 1 mm long, margin entire............................................ Lobelia hilaireana

– Latex white; inflorescence lax; bracteoles conspicuous, up to 10 mm long, margin ciliate ................................... Lobelia langeana