| 1 | Inflorescence of 1 or 2 pairs of flowers |
| 1' | Inflorescence usually of more than 2 pairs of flowers in a raceme or spike.... |
| 2 | Corolla more than 50 mm long |
| 2' | Corolla 20-50 mm long |
| 2'' | Corolla less than 20 mm long |
| 3 | Lateral bracts more or less connate but together not enclosing the ovary |
| 3' | Lateral bracts connate, together enclosing the ovary |
| 4 | Stem internodes quadrangular when young; leaves usually cordate at the base, subsessile |
| 4' | Stem internodes terete from youth; leaves usually cuneate at the base, petiolate. |
| 5 | Leaves widest below the middle; bracts not keeled |
| 5' | Leaves widest above the middle; bracts keeled |
| 6 | Flowers usually subsessile; lateral bracts connate, enclosing the ovary |
| 6' | Flowers usually pedicellate, sometimes very shortly; lateral bracts free or connate but not enclosing the ovary |
| 7 | Inflorescence normally a 2-flowered umbel |
| 7' | Inflorescence normally racemose or subumbellate, sometimes reduced to 2 flowers but usually with more |
| 8 | Lateral bracts free or nearly so, spreading; corolla in mature bud curved near the base, symmetrically winged |
| 8' | Lateral bracts connate, appressed to the ovary when young; corolla in mature bud curved above the middle, asymmetrically winged |
| 9 | Stem internodes two-edged when young; leaves usually cordate at the base and sessile |
| 9' | Stem internodes terete from youth; leaves cuneate or attenuate at the base, distinctly petiolate |
| 10 | Leaves glossy above, acuminate and acute at the apex, mostly more than 5 cm long and 2 cm wide; inflorescence umbellate |
| 10' | Leaves dull or lustrous above, mostly rounded at the apex, mostly less than 5 cm long and 2 cm wide; inflorescence racemose |
| 11 | Leaf lamina less than 5 cm long |
| 11' | Leaf lamina mostly more than 5 cm long |
| 12 | Corolla in mature bud crowned by a corona of dorsal appendages on the corolla lobes |
| 12' | Corolla in mature bud lacking a corona of dorsal appendages on the corolla lobes |
| 13 | Leaves rounded at the apex; ovary shortly tomentose and more or less tuberculate; the distal part of the corolla weakly to strongly papillose in bud |
| 13' | Leaves acute at the apex; ovary and corolla glabrous |
| 14 | Flowers usually subsessile |
| 14' | Flowers distinctly pedicellate |
| 15 | Leaf lamina more than 12 cm long; anther c. 5 mm long, longer than the free part of the filament |
| 15' | Leaf lamina less than 12 cm long; anther 1.5-2 mm long, much shorter than the free part of the filament |
| 16 | Corolla in mature bud more than 50 mm long |
| 16' | Corolla in mature bud 28-50 mm long |
| 16'' | Corolla in mature bud less than 28 mm long |
| 17 | Stem internodes quadrangular when young; leaves usually cordate at the base, subsessile |
| 17' | Stem internodes terete from youth; leaves usually cuneate at the base, petiolate |
| 18 | Leaf lamina more than 20 cm long, subsessile, bullate between the main veins; floral bracts 3-5 mm long |
| 18' | Leaf lamina mostly less than 20 cm long, mostly cuneate at the base and distinctly petiolate, smooth; floral bracts 1-3 mm long |
| 19 | Inflorescence of 1-4 pairs of flowers; axis 5-17 mm long, not subtended at the base by an involucre of short broadly triangular bracts; pedicels spreading, 3-7 mm long; bracts rounded, 1-2 mm long |
| 19' | Inflorescence of 2-7 pairs of flowers; axis 10-20 mm long, subtended at the base by an involucre of short broadly triangular bracts; pedicels appressed to the axis, 1-4 mm long; bracts keeled, acute, 2-3 mm long |
| 20 | Leaf lamina more than 15 cm long; free part of filament about 4 times as long as anther |
| 20' | Leaf lamina mostly less than 12 cm long; free part of filament 1.5-2 times as long as the anther |
| 21 | Stem internodes angular when young; leaves mostly cordate at the base and sessile; corolla more than 35 mm long |
| 21' | Stem internodes terete from youth; leaves mostly cuneate to truncate at the base and petiolate; corolla less than 35 mm long |
| 22 | Leaf lamina usually dull on both surfaces, rounded at the apex, attenuate at the base to a winged petiole |
| 22' | Leaf lamina glossy above, dull below, acuminate and mostly acute at the apex, shortly cuneate to truncate at the base to a sharply defined petiole |
| 23 | Leaf lamina more than 15 cm long; petiole mostly more than 15 mm long; free part of filament 3-5 times as long as the anther |
| 23' | Leaf lamina mostly less than 15 cm long; petiole mostly less than 15 mm long; free part of filament 1-3 times as long as the anther |
| 24 | Corolla tube more than 12 mm long |
| 24' | Corolla tube mostly less than 10 mm long |
| 25 | Leaf lamina usually dull on both surfaces, rounded at the apex, attenuate at the base to a winged petiole |
| 25' | Leaf lamina glossy above, dull below, acuminate and mostly acute at the apex, shortly cuneate to truncate at the base to a sharply defined petiole |
| 26 | Leaf lamina less than 6 cm long; the corolla about 7 mm long |
| 26' | Leaf lamina mostly more than 6 cm long; the corolla more than 8 mm long... |
| 27 | Stem internodes quadrangular when young; leaf lamina thick, mostly subsessile, mostly rounded towards the apex |
| 27' | Stem internodes terete from youth; leaf lamina coriaceous, distinctly petiolate, mostly attenuate or acuminate towards the apex |
| 28 | Corolla tube mostly red, about one fourth the corolla length; anther 2-3.5 mm long |
| 28' | Corolla tube mostly yellow or green, about one half the corolla length; anther 0.5-2 mm long |
