The Collaborative International Dictionary of English v.0.48:

Moonflower \Moon"flow`er\, n. (Bot.)
   (a) The oxeye daisy; -- called also moon daisy.
   (b) A kind of morning glory (Ipomoea Bona-nox) with large
       white flowers opening at night.
       [1913 Webster]

WordNet (r) 3.0 (2006):

moon daisy
    n 1: tall leafy-stemmed Eurasian perennial with white flowers;
         widely naturalized; often placed in genus Chrysanthemum
         [syn: oxeye daisy, ox-eyed daisy, marguerite, moon
         daisy, white daisy, Leucanthemum vulgare,
         Chrysanthemum leucanthemum]