%bogbean%

n. a perennial plant of Europe and America (Menyanthes trifoliata) having racemes of white or purplish flowers and intensely bitter trifoliate leaves; often rooting at the water margin and spreading across the surface; -- called also bog myrtle, water shamrock and marsh trefoil.
Syn. -- water shamrock, buckbean, bog myrtle, marsh trefoil. [ WordNet 1.5 ]