water clover

noun
  1. 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.
Also called pepperwort, water shamrock.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018