Nuphar advena

from WordNet (r) 3.0 (2006)

Nuphar advena
    n 1: common water lily of eastern and central North America,
         having broad leaves and globe-shaped yellow flowers; in
         sluggish fresh or slightly brackish water [syn:
         {spatterdock}, {cow lily}, {yellow pond lily}, {Nuphar
         advena}]

from The Collaborative International Dictionary of English v.0.48

Spatter-dock \Spat`ter-dock`\, n. (Bot.)
   The common yellow water lily ({Nuphar advena}).
   [1913 Webster]