The Collaborative International Dictionary of English v.0.48:

Verbena \Ver*be"na\, n. [L. See Vervain.] (Bot.)
   A genus of herbaceous plants of which several species are
   extensively cultivated for the great beauty of their flowers;
   vervain.
   [1913 Webster]

   Note: Verbena, or vervain, was used by the Greeks, the
         Romans, and the Druids, in their sacred rites.
         --Brewer.
         [1913 Webster]

   Essence of verbena, Oil of verbena, a perfume prepared
      from the lemon verbena; also, a similar perfume properly
      called grass oil. See Grass oil, under Grass.

   Lemon verbena, or Sweet verbena, a shrubby verbenaceous
      plant (Lippia citriodora), with narrow leaves which
      exhale a pleasant, lemonlike fragrance when crushed.
      [1913 Webster]

WordNet (r) 3.0 (2006):

verbena
    n 1: any of numerous tropical or subtropical American plants of
         the genus Verbena grown for their showy spikes of variously
         colored flowers [syn: verbena, vervain]