The Collaborative International Dictionary of English v.0.48:

Sea poppy \Sea" pop"py\ (Bot.)
   The horn poppy. See under Horn.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sea poppy
    n 1: yellow-flowered Eurasian glaucous herb naturalized in along
         sandy shores in eastern North America [syn: horn poppy,
         horned poppy, yellow horned poppy, sea poppy,
         Glaucium flavum]