| Plant | Low PPM | High PPM | StdDev | *Reference | |
|---|---|---|---|---|---|
| Rheum officinale | Root | -- | -- | Leung, A.Y., Encyclopedia of Common Natural Ingredients Used in Food, Drugs, and Cosmetics, John Wiley & Sons, New York, 1980. | |
| Rheum officinale | Plant | -- | 13000.0 | -0.5 | * |
| Ribes nigrum | Fruit Juice | -- | -- | * | |
| Ribes nigrum | Leaf | -- | -- | * | |
| Ribes nigrum | Fruit | -- | -- | * | |
| Ricinus communis | Leaf | -- | 2000.0 | -0.9 | * |
| Rosa multiflora | Fruit | -- | -- | * | |
| Rubus idaeus | Plant | -- | -- | Newall, C. A., Anderson, L. A. and Phillipson, J. D. 1996. Herbal Medicine - A Guide for Health-care Professionals. The Pharmaceutical Press, London. 296pp. | |
| Rumex acetosella | Shoot | -- | 5300.0 | -0.2 | * |
| Rumex acetosa | Leaf | -- | 12800.0 | -0.2 | * |
| Rumex crispus | Leaf | -- | -- | * | |
| Ruscus aculeatus | Plant | 300.0 | 400.0 | -0.7 | Pedersen, M. 1987. Nutritional Herbology. Pederson Publishing. Bountiful, Utah. 377 pp. |
| Ruscus aculeatus | Shoot | -- | -- | * | |
| Ruscus aculeatus | Root | 91.0 | 400.0 | * | |
| Ruta graveolens | Plant | -- | 20000.0 | -0.4 | * |
| Salix alba | Bark | -- | -- | Pedersen, M. 1987. Nutritional Herbology. Pederson Publishing. Bountiful, Utah. 377 pp. | |
| Salix alba | Leaf | -- | -- | * | |
| Sambucus canadensis | Leaf | 35000.0 | 38000.0 | 1.4 | * |
| Sambucus canadensis | Flower | 7700.0 | 52000.0 | 0.0 | * |
| Sambucus nigra | Leaf | 210.0 | 9200.0 | -0.4 | * |