Eriophorum vaginatum

from The Collaborative International Dictionary of English v.0.48

Hare's-tail \Hare's"-tail`\ (-t[=a]l`), n. (Bot.)
   A kind of grass ({Eriophorum vaginatum}). See {Cotton grass},
   under {Cotton}.
   [1913 Webster]

   {Hare's-tail grass} (Bot.), a species of grass ({Lagurus
      ovatus}) whose head resembles a hare's tail.
      [1913 Webster]