Source : Webster's Revised Unabridged Dictionary (1913)

Ragwort \Rag"wort`\, n. (Bot.)
   A name given to several species of the composite genus
   {Senecio}.

   Note: {Senecio aureus} is the golden ragwort of the United
         States: {S. elegans} is the purple ragwort of South
         Africa.

Source : WordNet®

ragwort
     n 1: widespread European weed having yellow daisylike flowers;
          sometimes an obnoxious weed and toxic to cattle if
          consumed in quantity [syn: {tansy ragwort}, {ragweed}, {benweed},
           {Senecio jacobaea}]
     2: American ragwort with yellow flowers [syn: {butterweed}, {Senecio
        glabellus}]