The Collaborative International Dictionary of English v.0.48:

Waterleaf \Wa"ter*leaf`\, n. (Bot.)
   Any plant of the American genus Hydrophyllum, herbs having
   white or pale blue bell-shaped flowers. --Gray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

waterleaf
    n 1: any of several plants of the genus Hydrophyllum