sea buckthorn

from The Collaborative International Dictionary of English v.0.48

Buckthorn \Buck"thorn`\, n. (Bot.)
   A genus ({Rhamnus}) of shrubs or trees. The shorter branches
   of some species terminate in long spines or thorns. See
   {Rhamnus}.
   [1913 Webster]

   {Sea buckthorn}, a plant of the genus {Hippopha["e]}.
      [1913 Webster]