The Collaborative International Dictionary of English v.0.48:

Gardenia \Garde"ni*a\, n. [NL.] (Bot.)
   A genus of plants, some species of which produce beautiful
   and fragrant flowers; Cape jasmine; -- so called in honor of
   Dr. Alexander Garden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gardenia
    n 1: any of various shrubs and small trees of the genus Gardenia
         having large fragrant white or yellow flowers