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Azolla cristata

Basic information
Scientific name Azolla cristata

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Major synonym A. microphylla, A. mexicana, A. caroliniana
Common names Water fern
Higher taxon Azollaceae, Hydropteridales, Filicopsida, Pteridophyta
Natural range North America, Central America, South America.
Habitat Fallow rice field, lake or pond, rice field, swamp.
Invasion information
Range in Japan Miyagi, Ibaraki, Gumma, Saitama, Tokyo, Aichi, Gifu, Ahiga, Kyoto, Osaka, Wakayama, Hyogo, Okayama, Hiroshima, Kagawa, Ehime, Tokushima, Fukuoka, and Saga Prefs. Range in Japan
Origin Unknown.
Date Spread since 1990s.
Route Deliberate: For agricultural use (rice-duck farming)
Accidental: Spread within Japan by hitchhiking on water bird body.
Impact Competition, hybridization, nutrient enrichment.
Native organism(s) affected: Native Azolla (A. imbricate and A. japonica) (competition, hybridization)
Freshwater communities (nutrient enrichment)
Regulation in Japan Import, transport and keeping are prohibited in Japan by the Invasive Alien Species Act.
Introduced range in other countries Unknown.
Reference Notes
  • JWRC (ed) (2008) A Photographic Guide to the Invasive Alien Species in Japan. Heibonsha, Tokyo (in Jpn)
  • Ministry of the Environment, Japan. The Invasive Alien Species Act (Accessed on 2011-12-13) (in Jpn)
  • etc.
The three species Azolla microphylla, A. mexicanaA. caroliniana are regarded as synonyms of A. cristata.