| a common freshwater fern, Marsilea quadrifolia, of lake edges and quiet ponds, having roots embedded in the bottom, very slender and often tangled stems, and floating, cloverlike leaves composed of four leaflets. |
| water shamrock | |
noun | |
| 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 |