Azolla cristata

Basic information
Scientific name	Azolla cristata	Click to magnify
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.
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) http://www.env.go.jp/en/nature/as.html (in Jpn) etc.	The three species Azolla microphylla, A. mexicana，A. caroliniana are regarded as synonyms of A. cristata.