hydrophyte

from WordNet (r) 3.0 (2006)

hydrophyte
    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

Hydrophyte \Hy"dro*phyte\, n. [Gr. ? + ? plant: cf. F.
   hydrophyte.]
   An aquatic plant; an alga.
   [1913 Webster]