saw-wort

from The Century Dictionary.

• noun A plant of the Old World genus Serratula, especially S. tinctoria, whose foliage yields a yellow dye. The name is derived from the sharp serration of the leaves. Species of Saussurea are also so called.
• noun The button-snakeroot, Laciniaria spicata.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) Any plant of the composite genus Serratula; -- so named from the serrated leaves of most of the species.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun European perennial whose serrate leaves yield a yellow dye