a bog plant (Menyanthes trifoliata) of the gentian family, with glossy leaves of three leaflets and white flowers; bogbean
See buckbean in American Heritage Dictionary 4
(bŭkˈbēnˌ)
noun
A perennial herb (Menyanthes trifoliata) native to the Northern Hemisphere and having trifoliate leaves and clusters of white, pink, or purplish flowers.