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Azolla pinnata R. Br., an Old World mosquito fern, was found to be naturalized in waterways of southern Florida near Jupiter in May 2007 (Bodle 2008). This tiny aquatic fern is native to a large area of the tropics, subtropics, and warm temperate regions of Africa, Asia, and Australia (Sweet & Hills 1971; PIER 2007). Azolla pinnata has fame as a promoted component of rice culture in China because of the nitrogen fixing symbiotic bacteria that live in its leaves (Moore 1969). The fern is a Federal Noxious Weed (Kay & Hoyle 2000) that was found to be naturalized in North Carolina in 1999, where it continues to have a presence (Bodle 2008). Azolla pinnata has also naturalized in New Zealand where it displaced the native A. rubra R.Br. in much of the country (PIER 2007). Another mosquito fern, the western North American native A. filiculoides Lamarck (Lumkin 1993), has invaded Europe and South Africa, where it became an important weed (Hill 1998). The source of the naturalized A. pinnata in Florida is unknown. The discovery of plants at an aquarium and water garden shop in North Carolina (Kay & Hoyle 2000) indicates either purposeful or accidental introduction through aquatic plant commerce as a likely source. Because of the problems that the invasive A. pinnata and A. filiculoides have caused elsewhere, and the problems caused by many other aquatic weeds, there was immediate concern about the potential weediness of A. pinnata in Florida when it was found. In the waterways where it was detected, it dominated the habitats (see photos in Bodle 2008). This invasive Azolla could diminish or displace the Florida native A. caroliniana Wild. (considered to be A. filiculoides by Evrard & van Hove 2004) and other valued native plants.