Azolla pinnata R.Br., Salviniaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

English: feathered waterfern, ferny azolla, greem azolla, mosquito fern, water velvet

Japanese: a-aka-ukikusa, b-aka-ukikusa, o-aka-ukikusa

Habit:  aquatic fern

Description:  "Plants small, 1.5 - 2.5 cm long, with a +/- straight main axis with pinnately arranged side branches, progressively longer towards the base, thus roughly triangular in shape, the basal branches themselves becoming pinnate and eventually fragmenting as the main axis decomposes to form new plants. Roots with fine lateral rootlets, having a feathery appearance in the water. Leaves minute, 1 -2 mm long, overlapping in 2 ranks, upper lobe green, brown green or reddish, lower lobe translucent brown; minute, short, pale, +/- cylindrical unicellular hairs often present on the upper lobes. When fertile, round sporocarps 1 - 1.5 mm wide can be seen on the under side at the bases of the side branches. The leaves often have a maroon-red tinge and the water can appear to be covered by red velvet from the distance. The upper surface of the leaves are totally water-repellant, and if completely submerged the plants quickly refloat with the right side up." (Croft, 1986).

Habitat/ecology:  "It is found in tropical regions and in lakes, marshes, ponds, paddy fields, ditches and rivers of warm temperature.  Wave and wind action reduce growth and fragment the plants, thus it seldom occurs in large lakes or rapidly moving water.  Because it is not dependent upon N in the water and is free-floating, it can inhabit areas other weeds cannot" (Holm et al., 1997; p. 95).  Forms dense mats that choke out other species.

Propagation:  Spores and vegetatively.  "Its rapid expansion under proper environmental conditions is the result of vegetative reproduction that occurs when an abscission layer forms at the base of lateral rhizome, allowing it to separate from the main rhizome.  A small root is present on the detached branch" (Holm et al., 1997; p. 96).

Native range:  "Africa and Madagascar, India, Southeast Asia, China and Japan, Malaya and the Philippines, the New Guinea mainland and Australia."  (Croft, 1986)

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Marshall Islands Ratak Chain	Majuro (Mãjro) Atoll	introduced	Vander Velde, Nancy (2003) (p. 14) Rare or now extirpated.
New Caledonia New Caledonia	New Caledonia Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines Philippine Islands	Philippine Islands	native	Waterhouse, D. F. (1993) (pp. 63, 76)

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 (2013)
Australia Australia (continental)	Australia (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013) Victoria
Australia Australia (continental)	Northern Territory	native	Australian Biological Resources Study (2013)
Australia Australia (continental)	Queensland	native	Australian Biological Resources Study (2013)
Cambodia Cambodia	Cambodia (Kingdom of)	native	Waterhouse, D. F. (1993) (pp. 63, 76)
China China	China (People's Republic of)	native cultivated	U.S. Dept. Agr., Agr. Res. Serv. (2013) Anhui, Fujian, Henan, Hubei, Jiangsu, Jiangxi, Sichuan, Zhejiang
Indonesia Indonesia	Indonesia (Republic of)	native	Waterhouse, D. F. (1993) (pp. 63, 76)
Japan Japan	Japan	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South Korea South Korea	South Korea (Republic of)		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 93)
Malaysia Malaysia	Malaysia (country of)	native	Waterhouse, D. F. (1993) (pp. 63, 76)
Negara Brunei Darussalam Brunei	Brunei (Negara Brunei Darussalam)	native	Waterhouse, D. F. (1993) (pp. 63, 76)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 36) "Ponds and lakes".
Singapore Singapore	Singapore (Republic of)	introduced invasive	Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 17) Naturalised
Thailand Thailand	Thailand (Kingdom of)	native	Waterhouse, D. F. (1993) (pp. 63, 76)
Vietnam Vietnam	Vietnam (Socialist Republic of)	native cultivated	Waterhouse, D. F. (1993) (pp. 63, 76)

Comments:  On US noxious weed list.

In New Zealand, Azolla pinnata has replaced a native floating fern, Azolla rubra, over most of northern New Zealand (Owen, 1997).

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.

Control:  If you know of control methods for Azolla pinnata, please let us know.