WordNet (r) 3.0 (2006):

floating fern
    n 1: pantropical aquatic fern [syn: floating fern,
         Ceratopteris thalictroides]
    2: aquatic fern of tropical America often used in aquariums
       [syn: floating fern, water sprite, Ceratopteris
       pteridioides]
    3: small free-floating aquatic fern from the eastern United
       States to tropical America; naturalized in western and
       southern Europe [syn: mosquito fern, floating fern,
       Carolina pond fern, Azolla caroliniana]