The Collaborative International Dictionary of English v.0.48:

Saw-wort \Saw"-wort`\, n. (Bot.)
   Any plant of the composite genus Serratula; -- so named
   from the serrated leaves of most of the species.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sawwort
    n 1: European perennial whose serrate leaves yield a yellow dye
         [syn: sawwort, Serratula tinctoria]