Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.
| 1 Low, erect or ascending herb or (Aristolochia pentandra) a twining herbaceous vine; leaves 0.5-6.5 cm wide. |
| ..2 Leaf bases cuneate; gynoecium and androecium 5-merous |
| ..2 Leaf bases cordate; gynoecium and androecium 3-, 5-, or 6-merous. |
| ....3 Twining herbaceous vine; gynoecium and androecium 5-merous |
| ....3 Erect or ascending herb; gynoecium and androecium 3- or 6-merous. |
| ......4 Leaf blade as wide as long, or wider than long; leaf venation palmate |
| ......4 Leaf blade narrower than long; leaf venation pinnate (3-veined from the base, pinnate above) |
| 1 Woody, twining vine; leaves 3-35 cm wide |
| ........5 Gynostemium lobes 3; calyx limb 3-lobed, the lobes similar in size and shape and arranged radially around the tube orifice at 120 degree angles |
| ........5 Gynostemium lobes 6; calyx limb 1- or 2-lobed (if 2-lobed, the lobes dissimilar in shape) |
| ..........6 Leaf base rounded to truncate; leaf venation pinnate |
| ..........6 Leaf base cordate; leaf venation palmate. |
| ............ 7 Calyx limb 1-lobed, orbicular, 10-50 cm in diameter |
............ ..8 Calyx limb about 10 cm in diameter, notched at the bottom |
| ............ ..8 Calyx limb 20-50 cm in diameter, attenuate at the bottom into an elongate dangling appendage |
| ............ 7 Calyx limb 2-lobed, the lower lanceolate, acuminate, folded longitudinally and bird-beak-like, 10-20 cm long, the upper with a parallel-sided claw and orbicular tip. |
| ............ ....9 Upper lobe of calyx limb 14-18 cm wide, with ruffled margin, pendent below the lower lip |
| ............ ....9 Upper lobe of calyx limb 4-5 cm wide, not ruffled, erect over the lower lip |