| 1 | Anthers finely acuminate and acute |
| 1' | Anthers blunt, sometimes broadly acute but not acuminate |
| 2 | Corolla 55-90 mm long |
| 2' | Corolla 18-55 mm long |
| 3 | Bracts longer than the ovary; flowers closely sessile; inflorescence and flowers with a dense long loose indumentum |
| 3' | Bracts shorter than the ovary; flowers shortly pedicellate; inflorescence and flowers with a close tomentum or glabrescent |
| 4 | Indumentum ochre to red-brown; stems robust; lamina 10-25 cm long; corolla less than 30 mm long |
| 4' | Indumentum white to light ochre; stems slender; lamina mostly 5-10 cm long; corolla usually more than 30 mm long |
| 5 | Inflorescence axis normally more than 40 mm long and bearing more than 20 flowers |
| 5' | Inflorescence axis up to 30 mm long and bearing up to 20 flowers |
| 6 | Corolla less than 50 mm long |
| 6' | Corolla more than 50 mm long |
| 7 | Inflorescence and flowers entirely glabrous; corolla mostly more than 30 mm long |
| 7' | Inflorescence and flowers sparsely to densely ochre- to red-brown-tomentose; corolla mostly less than 30 mm long |
| 8 | Leaves thickly coriaceous, bullate between the depressed midrib and lateral veins; anther much shorter than the free part of the filament; corolla split to near the middle at anthesis |
| 8' | Leaves thinly coriaceous, not bullate; veins not depressed; anther ± equal to the free part of the filament; corolla split almost to the base at anthesis. |
| 9 | Corolla densely tomentose, lacking knobs on the petals; leaf lamina relatively thin |
| 9' | Corolla in mature bud glabrous or nearly so, with a knob on each petal just below the neck; leaf lamina relatively thick |
| 10 | Corolla tube regular, inflated and more or less bell-shaped |
| 10' | Corolla tube more or less curved, slender or weakly inflated, gradually widened upwards, usually split more deeply on one side |
| 11 | Leaves linear to narrow lanceolate, pendulous; corolla 4-merous, in mature bud not winged or longitudinally ribbed in the inflated part; inflorescence a false umbel of 2 or 3 flowers of almost equal age |
| 11' | Leaves elliptic to ovate or obovate, spreading; corolla 5- or rarely 4-merous, in mature bud winged or longitudinally ribbed in the inflated part; inflorescence a few- to several-flowered raceme, sometimes subumbellate |
| 12 | Corolla glabrous or nearly so; fruit warty; inflorescence 2- to 4-flowered |
| 12' | Corolla sparsely to densely white or grey (rarely brown) tomentose; fruit smooth; inflorescence usually 6- to 12-flowered |
| 13 | Inflorescences several, clustered at enlarged gall-like leafless nodes |
| 13' | Inflorescences solitary or few, in leaf axils or at younger leafless nodes |
| 14 | Leaves thin, undulate at margin when dry, with slender petiole |
| 14' | Leaves thick, not undulate at margin when dry, with a thick winged petiole.... |
| 15 | Corolla less than 20 mm long |
| 15' | Corolla 20-30 mm long |
| 15'' | Corolla more than 30 mm long |
| 16 | Inflorescence and flowers with a persistent thick red-brown indumentum; corolla in mature bud more or less cylindric |
| 16' | Inflorescence and flowers with a short tomentum, the corolla glabrescent; corolla in mature bud with a distinct neck |
| 17 | Corolla 4-merous, obtuse in mature bud |
| 17' | Corolla 5-merous, attenuate towards an acute apex in mature bud |
| 18 | Leaves opposite, sessile, cordate at the base |
| 18' | Leaves mostly scattered, petiolate, not cordate at the base |
| 19 | Leaves usually darker and more lustrous on the upper surface... |
| 19' | Leaves dull on both sides |
| 20 | Inflorescence entirely glabrous; calyx limb truncate |
| 20' | Inflorescence and flowers white tomentose, especially the ovary; calyx limb distinctly toothed |
