Definition of water fern in US English:

water fern

noun

  • 1A small aquatic or semiaquatic fern which is either free-floating or anchored by the roots, found chiefly in tropical and warm countries.

    Families Azollaceae, Marsileaceae and Salviniaceae: many species, in particular the minute floating Azolla filiculoides of tropical America, which has been naturalized elsewhere

    • ‘Avoid rampant non-natives species such as Canadian pond weed and rapidly spreading duckweeds and water ferns.’
    • ‘Genomic downsizing is suggested for the heterosporous water ferns and for the aquatic fern Ceratopteris.’
    • ‘However, both water ferns and Selaginella are also heterosporous, unlike any other pteridophytes except Isoetales.’
    • ‘Thick mass of Trapa, an economically important free floating plant called Singhari by the local people, besides water ferns, duckweeds etc can be seen almost everywhere.’
  • 2An Australian fern with large coarse fronds, typically growing in marshy areas and rainforests.

    Genus Blechnum, family Blechnaceae: several species