Ecology: Plants reproduce vegetatively and sexually. Vegetative fragments form when the main axis deteriorates and lateral branches break free (Rao 1935; Shen 1960; Lumpkin 1983). When reproducing sexually, round sporocarps (1-1.5 mm in diameter) form on the underside of the leaves (Rao 1935; Shen 1960; Lumpkin 1983).
Azolla pinnata grows optimally between 29-33ºC, although only subspecies asiatica was studied (Watanbe and Berja 1983). It tolerates salt concentrations up to 30 mM, but can be preincubated in lower concentrations to increase salinity tolerance up to as high as 60 mM (Rai and Rai 1999).
Upper lobes of A. pinnata's leaves are host to a cyanobacteria symbiont that fixes atmospheric nitrogen (Strasburger 1873; Moore 1969; Wagner 1997). It is sometimes introduced by rice farmers as a natural fertilizer for this reason (Lumpkin and Plucknett 1980). Typical habitats are wind-protected, slow-moving waters, such as ponds, small lakes, swamps, wetlands or drainage canals (Svenson 1944).
References: (click for full references)
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Bodle, M. 2008. Feathered mosquito fern (Azolla pinnata R. Br.) comes to Florida. Aquatics 30(2):4,6,8-9. http://www.fapms.org/aquatics/issues/2008summer.pdf.
Center for Invasive Species and Ecosystem Health. 2015. EDDMapS: Early detection and distribution mapping system. The University of Georgia, Tifton, GA. http://www.eddmaps.org.
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Lumpkin, T.A., and D.L. Plucknett. 1980. Azolla: botany, physiology, and use as a green manure. Economic Botany 34(2):111-153.
Lumpkin, T.A. 1983. Taxonomy, physiology, and agronomic potential of Azolla spp. Unpublished Ph.D. dissertation. University of Hawaii, Honolulu, HI.
Madeira, P.T., T.D. Center, J.A. Coetzee, R.W. Pemberton, M.F. Purcell, and M.P. Hill. 2013. Identity and origins of introduced and native Azolla species in Florida. Aquatic Botany 111:9-15.
Madsen, J.D. 2010. Invasive Plant Atlas of the MidSouth. Geosystems Research Institute, Mississippi State University, Starkville, MS. http://www.gri.msstate.edu/ipams/.
Moore, A.W. 1969. Azolla: biology and agronomic significance. Botanical Review 35(1):17-34.
Pemberton, R.W., and J.M. Bodle. 2009. Native North American azolla weevil, Stenopelmus rufinasus (Coleoptera: Curculionidae), uses the invasive old world Azolla pinnata as a host plant. Florida Entomologist 92(1):153-155.
Pereira, A.L., M. Martins, M.M. Oliveira, and F. Carrapiço. 2011. Morphological and genetic diversity of the family Azollaceae inferred from vegetative characters and RAPD markers. Plant Systematics and Evolution 297:213-226.
Rai, V., and A.K. Rai. 1999. Growth behaviour of Azolla pinnata at various salinity levels and induction of high salt tolerance. Plant and Soil 206:79-84.
Rao, H.S. 1935. The structure and life-history of Azolla pinnata R. Brown with remarks on the fossil history of the hydropterideæ. Proceedings of the Indian Academy of Sciences - Section B 2(2):175-200. https://www.ias.ac.in/article/fulltext/secb/002/02/0175-0201.
Saunders, R.M.K, and K. Fowler. 1992. A morphological taxonomic revision of Azolla Lam. section Rhizosperma (Mey.) Mett. (Azollaceae). Botanical Journal of the Linnean Society 109(3):329-357.
Shen, E.Y. 1960. Anabaena azollae and its host Azolla pinnata. Taiwania 7:1-7.
Strasburger, E. 1873. Ueber Azolla. Hermann Davis, Jena, Germany.
Svenson, H.K. 1944. The new world species of Azolla. American Fern Journal 34(3):69-84.
Sweet, A., and L.V. Hills. 1971. A study of Azolla pinnata R. Brown. American Fern Journal 61(1):1-13.
Thomas, K.A., and P. Guertin. 2007. Southwest Exotic Mapping Program 2007: occurrence summary and maps of select invasive non-native plants in Arizona. US Geological Survey Open-File Report 2007-1277. http://pubs.usgs.gov/of/2007/1277/.
Wagner, G.M. 1997. Azolla: a review of its biology and utilization. Botanical Review 63(1):1-26.
Watanabe, I., and N.S. Berja. 1983. The growth of four species of Azolla as affected by temperature. Aquatic Botany 15:175-185.
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.