| Plant | Low PPM | High PPM | StdDev | *Reference | |
|---|---|---|---|---|---|
| Cinchona spp | Bark | -- | -- | List, P.H. and Horhammer, L., Hager's Handbuch der Pharmazeutischen Praxis, Vols. 2-6, Springer-Verlag, Berlin, 1969-1979. | |
| Frangula purshiana | Plant | -- | -- | * | |
| Aspidosperma quebracho-blanco | Bark | -- | -- | * |