| 1 | Herbs, sometimes with a woody base |
| 1' | Trees or shrubs or climbers |
| 2 | Leaves spirally arranged |
| 2' | Leaves opposite or in whorls |
| 3 | Leaves narrowly oblong, < 1 cm wide |
| 3' | Leaves obovate or elliptic, > 2 cm wide |
| 4 | Succulent shrub; corolla tube wide; anthers with long bristly appendages |
| 4' | Small trees; corolla tube narrow; anthers without long bristly appendages |
| 5 | Leaf blade rounded at apex, dark green, shiny above |
| 5' | Leaf blade acute or acuminate at apex, glaucous, dull above |
| 6 | Corolla tube not yellow, < 3 cm long; anthers with long appendages |
| 6' | Corolla tube yellow, infundibuliform, > 3.5 cm long, anthers without appendages |
| 7 | Sepals without colleters inside; lower, narrow corolla tube about equal in length to upper, wider corolla tube |
| 7' | Sepals with colleters inside; lower, narrow corolla tube much shorter than upper, wider corolla tube |
