| 1 | Corolla tube inflated near insertion of stamens, corolla lobes recurved; flowers cream to white |
| 1' | Corolla tube not inflated (but see also under V. rosea), corolla lobes patent or ascending; flowers white or differently coloured |
| 2 | Flowers blue, nodding; roots tuberous, forming dense clumps and oriented like the rays of a star |
| 2' | Flowers if blue never nodding; root system differently shaped (but compare V. flavescens) |
| 3 | Stems purple to red; corolla lobes acuminate to caudate, purple to blue |
| 3' | Stems differently coloured; corolla lobes acute to obtuse, rarely acuminate (V. acuminata), rarely purple to blue (V. caerulea) |
| 4 | Calyx tube often split for most of its length along 1 or 2 sides; corolla blue to purplish (often fading to white) |
| 4' | Calyx not split, entire, 5-lobed; corolla not blue |
| 5 | Flowers < 25 mm long |
| 5' | Flowers > 25 mm long |
| 6 | Flowers solitary; corolla yellow (rarely white to flesh-coloured) |
| 6' | Inflorescence several-flowered; corolla white, yellow, or orange |
| 7 | Thecae with a basal, tail-like, densely hairy appendage; flowers often 4-merous |
| 7' | Thecae without a basal, tail-like, densely hairy appendage; flowers always 5-merous |
| 8 | Corolla white to pale pink; calyx 2.5-6 mm long |
| 8' | Corolla yellow to orange; calyx 5-9 mm long |
| 9 | Corolla yellow; seeds filiform |
| 9' | Corolla differently coloured; seeds globose |
| 10 | Calyx 30-40 mm long; corolla lobes ascending, white, mauve, or pink |
| 10' | Calyx 6-15 mm long; corolla lobes patent, white, pink, or red |
| 11 | Calyx 12-15 mm long; corolla lobes white, acuminate |
| 11' | Calyx 6-12 mm long; corolla lobes pink to red, obtuse |
