Azolla filiculoides Lam., Salviniaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

English: azolla, ferny azolla, large mosquito fern

Habit:  aquatic fern

Description:  "Plants green to yellowish green or dark red, with 2 growth stages; plants fertile only in mature stage, generally in late spring. Stems prostrate when immature, 1--3 cm, internodes elongate to 5 mm, becoming nearly erect to 5 cm or more when mature and crowded. Hairs on upper leaf lobes strictly unicellular. Megaspores warty with raised angular bumps, each with a tangle of filaments" (Flora of North America).

Habitat/ecology:  Taro patches, lakes, ponds, ditches, canals, marshes, and slow-moving streams. Forms dense mats that choke out other species. Azolla lives in symbiosis with blue-green algae (cyanobacteria), taking advantage of their ability to fix nitrogen.  It is sometimes introduced and used by farmers as a natural fertilizer for this reason.  It has also been introduced to assist in mosquito abatement.  In Hawai‘i, "now well established in flooded areas on all the islands"  (Wilson, 1996).

Propagation:  "The fern spreads rapidly by fragmentation of the plant.  Sexual reproduction is common as well, and the spores are extremely resistant to desiccation" (Weber, 2003; p. 64).

Native range:  Western North America (Flora of North America)

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Cook Islands Southern Cook Islands	Mangaia Island	introduced invasive	Space, James C./Flynn, Tim (2002) (p. 13)
Cook Islands Southern Cook Islands	Mangaia Island		Sykes, Bill (year unknown)
Cook Islands Southern Cook Islands	Ma‘uke Island	introduced invasive	Space, James C./Flynn, Tim (2002) (p. 13)
Cook Islands Southern Cook Islands	Ma‘uke Island		Sykes, Bill (year unknown)
Cook Islands Southern Cook Islands	Rarotonga Island	introduced invasive	Space, James C./Flynn, Tim (2002) (p. 13)
Cook Islands Southern Cook Islands	Rarotonga Island		Sykes, Bill (year unknown)
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wilson, Kenneth A. (2003) (p. 5) Voucher cited: Imada 99-16 (BISH)
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, W. L./Herbst, D. R./Lorence, D. H. (2005)
State of Hawaii Hawaiian Islands	Kaho‘olawe Island		Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wagner, W. L./Herbst, D. R./Lorence, D. H. (2005)
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Wagner, W. L./Herbst, D. R./Lorence, D. H. (2005)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, W. L./Herbst, D. R./Lorence, D. H. (2005)
State of Hawaii Hawaiian Islands	Moloka‘i Island	introduced invasive	Wagner, W. L./Herbst, D. R./Lorence, D. H. (2005)
State of Hawaii Hawaiian Islands	Ni‘ihau Island		Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, W. L./Herbst, D. R./Lorence, D. H. (2005)

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	New South Wales	native	Australian Biological Resources Study (2011)
Australia Australia (continental)	Queensland	native	Australian Biological Resources Study (2011)
Canada Canada	Canada (country)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Chile (continental) Chile	Chile (Republic of)	native	Belov, Michail (2011)
Colombia Colombia	Colombia (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Costa Rica Costa Rica	Costa Rica (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Ecuador (Mainland) Ecuador	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Guatemala Guatemala	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Honduras Honduras	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 41)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 36) "Slow moving streams, ponds and lakes".
Nicaragua Nicaragua	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Perú Perú	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
United States (continental except west coast) United States (other states)	United States (other states)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

Comments:  Reportedly introduced to the Cook Islands as a nitrogen supplement in Taro patches (Bill Sykes, pers. com.). In Hawai‘i, "deliberately brought into the Islands as part of a mosquito abatement program in rice fields" (Wilson, 1996).

Control: 

Physical:  "Mechanical control includes removing plants by fine meshed nets.  However, the plant can re-establish from spores, and manual removal may be impractical for large infestations".

Chemical:  "Herbicides used include glyphosate, paraquat, or diquat.  A follow-up program is needed to control new plants germinating from spores"  (Weber, 2003; p. 64).

Additional information:
Photos and other information from Chileflora.

Additional online information about Azolla filiculoides is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Azolla filiculoides as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Azolla filiculoides may be available from the Germplasm Resources Information Network (GRIN).

References:

Australian Biological Resources Study. 2011. Flora of Australia Online. Australian Biological Resources Study, Canberra.

Belov, Michail. 2011. Chileflora (online resource).

Flora of North America Editorial Committee, eds. 2011. Flora of North America North of Mexico (online edition).

Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. 1979. A geographical atlas of world weeds. John Wiley & Sons, New York. 391 pp.

Space, James C./Flynn, Tim. 2002. Report to the Government of the Cook Islands on invasive plant species of environmental concern. USDA Forest Service, Honolulu. 146 pp.

Staples, George W./Herbst, Derral R. 2005. A tropical garden flora: plants cultivated in the Hawaiian Islands and other tropical places. Bishop Museum Press, Honolulu. 908 pp.

Sykes, Bill. 0. Bill Sykes, pers. com.

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

Wagner, W. L./Herbst, D. R./Lorence, D. H. 2005. Flora of the Hawaiian Islands website (online resource).

Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. 1988. Flora of New Zealand, Volume IV: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch. 1365 pp.

Weber, Ewald. 2003. Invasive plants of the World. CABI Publishing, CAB International, Wallingford, UK. 548 pp.

Wilson, K. A. 1996. Alien ferns in Hawai‘i. Pacific Science. 50(2):127-141.

Wilson, Kenneth A. 2003. New records of alien pteridophytes for Hawai‘i. In: Evenhuis, Neal L. and Eldredge, Lucius G., eds. Records of the Hawaii Biological Survey for 2001-2002. Part 2: Notes. Bishop Museum Occasional Papers. 74:5-7.