Data Views Total Plants: 2 CSV Excel PDF Click on column headings to sort table by that column Plant Part Low PPM High PPM StdDev *Reference Echinacea angustifolia Root -- 298.5 1.0 Jim Duke's personal files. Echinacea purpurea Root -- 166.7 -1.0 Jim Duke's personal files. *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.