Sweet leaf, Stevia rebaudiana, a natural sweetener. Close up showing serrated leaves.

Sweet leaf, Stevia rebaudiana, a natural sweetener. Close up showing serrated leaves.

Sweet leaf, Stevia rebaudiana, a natural sweetener. Close up showing serrated leaves.

Sweet leaf, Stevia rebaudiana, a natural sweetener. Close up showing serrated leaves.

Sweet leaf, Stevia rebaudiana, a natural sweetener. Close up showing serrated leaves.

Sweet leaf, Stevia rebaudiana, a natural sweetener. Close up showing serrated leaves.

Chinese meadow rue, Thalictrum delavayi showing delicate flower panicles.

Chinese meadow rue, Thalictrum delavayi showing delicate flower panicles.

St John's wort, Hypericum perforatum, close up showing clusters of the yellow flowers with protruding stamens against dark green background.

St John's wort, Hypericum perforatum, close up showing clusters of the yellow flowers with protruding stamens against dark green background.

St John's wort, Hypericum perforatum, showing clusters of the yellow flowers with protruding stamens against dark green background.

St John's wort, Hypericum perforatum, showing clusters of the yellow flowers with protruding stamens.