The Collaborative International Dictionary of English v.0.48:

leopard's bane \leop"ard's bane`\ (l[e^]p"[~e]rdz b[=a]n`) n.
   (Bot.)
   A name of several harmless plants, as Arnica montana
   (Arnica acaulis syn. Doronicum acaule), Senecio
   Doronicum, and Paris quadrifolia.

   Syn: leopardbane, leopard's-bane.
        [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

leopardbane \leop"ard*bane\ (l[e^]p"[~e]rd*b[=a]n`), n.
   Any of several herbs of the genus Doronicum (as Doronicum
   acaule syn. Arnica acaulis) having alternate often
   clasping stem leaves cultivated for their long stalks of
   yellow flower heads. See leopard's bane.

   Syn: leopard's-bane, leopard's bane.
        [WordNet 1.5 +PJC]

   false" leop`ard*bane (f[add]ls" l[e^]p`[~e]rd*b[=a]n`), n.
      Any of several herbs of the genus Doronicum, such as the
      great false leopardbane (Doronicum pardalianches) of
      North America and the oriental false leopardbane
      (Doronicum orientale syn. Doronicum caucasicum).
      [PJC]