| Plant | Low PPM | High PPM | StdDev | *Reference | |
|---|---|---|---|---|---|
| Quisqualis indica | Fruit | -- | 13.0 | 0.0 | * |
| Raphanus sativus | Root | 0.3 | 8.0 | -0.4 | * |
| Raphanus sativus | Seed | -- | 6.0 | -0.8 | * |
| Rehmannia glutinosa | Root | -- | 4.0 | -0.9 | * |
| Rheum palmatum | Rhizome | 6.0 | 10.0 | -0.1 | * |
| Rheum rhabarbarum | Pt | 0.2 | 5.2 | -1.0 | * |
| Rhizophora mangle | Leaf | -- | 35.0 | 0.2 | * |
| Rhus copallina | Leaf | 0.8 | 19.0 | -0.2 | * |
| Rhus glabra | Stem | 0.6 | 20.0 | -0.5 | * |
| Rhus copallina | Stem | 1.8 | 30.0 | -0.5 | * |
| Ribes nigrum | Fruit | 0.6 | 7.0 | -0.5 | * |
| Ribes uva-crispa | Fruit | 0.4 | 6.0 | -0.5 | * |
| Ribes rubrum | Fruit | 0.5 | 7.0 | -0.5 | * |
| Rosa canina | Fruit | 1.8 | 36.0 | 1.8 | * |
| Rosa laevigata | Fruit | 8.0 | 9.0 | -0.3 | * |
| Rosmarinus officinalis | Plant | 5.0 | 6.0 | -0.9 | USDA's Ag Handbook 8 and sequelae) |
| Rosmarinus officinalis | Leaf | 3.0 | 19.0 | -0.2 | USDA's Ag Handbook 8 and sequelae) |
| Rubia cordifolia | Root | -- | 15.0 | 0.4 | * |
| Rubus chingii | Fruit | -- | 12.0 | -0.1 | * |
| Rubus chamaemorus | Fruit | 0.7 | 5.6 | -0.6 | * |