Chrysophanic

a.
  1. Pertaining to, or derived from, or resembling, chrysophane.
    2. Chrysophanic acid (Chem.),
    a yellow crystalline substance extracted from rhubarb, yellow dock, sienna, chrysarobin, etc., and shown to be a derivative of an anthracene. It is used in the treatment of skin diseases; -- called also rhein, rheic acid, rhubarbarin, etc.