Synonyms for Water Shamrock (same or very similar meaning)
WordNet sense 1 (perennial plant of Europe and America having racemes of white or purplish flowers and intensely bitter trifoliate leaves; often rooting at water margin and spreading across the surface):
bogbean, buckbean, bog myrtle, marsh trefoil, Menyanthes trifoliataFrom the ODE community, based on WordNetadd/edit