Data Views Total Plants: 2 CSV Excel PDF Click on column headings to sort table by that column Plant Part All Bark Rhizome Low PPM High PPM StdDev *Reference Rheum palmatum Rhizome -- -- * Frangula purshiana Bark -- -- * *Unless otherwise noted all references are to Duke, James A. 1992. Handbook of phytochemical constituents of GRAS herbs and other economic plants. Boca Raton, FL. CRC Press.