member of the flowering plant family Menyanthaceae of the order Asterales, consisting of 5 genera and 58 species of aquatic or marsh herbs with creeping stems, native to temperate areas of the world. Some species have single leaves that alternate along the stem; others have leaves composed of three leaflets that have sheathing leafstalks.

Buckbean, or bogbean (Menyanthes trifoliata), a medicinal plant of wet soils, has white or pink flowers, bitter-tasting leaves, and hard, light brown seeds. The species of fringed water lily, water snowflake, and floating heart (Nymphoides)—all submerged plants with buried rootstalks and floating leaves—have yellow or white flowers.