water plant

from WordNet (r) 3.0 (2006)

water plant
    n 1: a plant that grows partly or wholly in water whether rooted
         in the mud, as a lotus, or floating without anchorage, as
         the water hyacinth [syn: {aquatic plant}, {water plant},
         {hydrophyte}, {hydrophytic plant}]

from The Collaborative International Dictionary of English v.0.48

Water plant \Wa"ter plant`\
   A plant that grows in water; an aquatic plant.
   [1913 Webster]