| | 1. Sinuses between corolla lobes with a variously shaped, sometimes fringed appendage, or ± truncate (base of sinus generally > 1 mm wide) |
| GENTIANA |
| | 1' Sinuses between corolla lobes unappendaged and acutely tapered |
| |
| | 2. Corolla ± rotate, rarely bell-shaped, lobed ± to base, nectary pits prominent, margins fringed |
| SWERTIA |
| | 2' Corolla not rotate, with distinct tube, nectary pits 0 (but corollas sometimes bearing fringes or scales) |
| |
| | 3. Corolla > 2 cm, widely bell-shaped; corolla lobes >> tube |
| EUSTOMA (no key) |
| | 3' Corolla generally < 2 cm, not widely but sometimes narrowly ± bell-shaped; corolla lobes < or = tube |
| |
| | 4. Corolla < 1 cm, pink or yellow, lobes without fringes or scales on inner surface |
| |
| | 5. Calyx very deeply lobed, closely appressed to corolla tube |
| CENTAURIUM |
| | 5' Calyx shallowly lobed, much wider than corolla tube |
| CICENDIA (no key) |
| | 4' Corolla generally > 1 cm, blue to violet, rarely white, lobes with or without fringes or scales on inner surface near base |
| |
| | 6. Corolla < 2 cm, lobes ± entire, with fringes or scales on inner surface near base |
| GENTIANELLA |
| | 6' Corolla > 2 cm, lobes ± entire to conspicuously serrate, jagged, or fringed, without fringes or scales on inner surface |
| GENTIANOPSIS
|