The Collaborative International Dictionary of English v.0.48:

Shasta daisy \Shasta daisy\
   A large-flowered garden variety of the oxeye daisy.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

shasta daisy
    n 1: hybrid garden flower derived from Chrysanthemum maximum and
         Chrysanthemum lacustre having large white flower heads
         resembling oxeye daisies; often placed in the genus
         Chrysanthemum [syn: shasta daisy, Leucanthemum
         superbum, Chrysanthemum maximum maximum]