The Collaborative International Dictionary of English v.0.48:

Lizard's tail \Liz"ard's tail`\n. (Bot.)
   A perennial plant of the genus Saururus (Saururus
   cernuus), growing in marshes, and having white flowers
   crowded in a slender terminal spike, somewhat resembling in
   form a lizard's tail; whence the name. --Gray.
   [1913 Webster]