The Collaborative International Dictionary of English v.0.48:

maltese cross \maltese cross\ n. (Bot.)
   A Eurasian garden perennial (Lychins chalcedonica) having
   scarlet flowers in dense terminal heads.

   Syn: scarlet lychnis, Lychins chalcedonica.
        [WordNet 1.5]

   2. A cross with triangular or arrow-shaped arms and the
      points toward the center. See illustration under cross.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

Lychins chalcedonica
    n 1: Eurasian garden perennial having scarlet flowers in dense
         terminal heads [syn: scarlet lychnis, maltese cross,
         Lychins chalcedonica]