The Collaborative International Dictionary of English v.0.48:

Danewort \Dane"wort`\, n. (Bot.)
   A fetid European species of elder (Sambucus Ebulus); dwarf
   elder; wallwort; elderwort; -- called also Daneweed,
   Dane's weed, and Dane's-blood.

   Note: [Said to grow on spots where battles were fought
         against the Danes.]
         [1913 Webster]