The Collaborative International Dictionary of English v.0.48:

Horsetail \Horse"tail`\, n.
   1. (Bot.) A leafless plant, with hollow and rushlike stems.
      It is of the genus Equisetum, and is allied to the
      ferns. See Illust. of Equisetum.
      [1913 Webster]

   2. A Turkish standard, denoting rank.
      [1913 Webster]

   Note: Commanders are distinguished by the number of
         horsetails carried before them. Thus, the sultan has
         seven, the grand vizier five, and the pashas three,
         two, or one.
         [1913 Webster]

   Shrubby horsetail. (Bot.) See Joint-fir.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Joint-fir \Joint"-fir`\, n. (Bot.)
   A genus (Ephedra) of leafless shrubs, with the stems
   conspicuously jointed; -- called also shrubby horsetail.
   There are about thirty species, of which two or three are
   found from Texas to California.
   [1913 Webster]