Spirodela polyrhiza (L.) Schleid., Araceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

Chinese: zi ping

English: giant duckweed, great duckweed, greater duckweed, large duckweed, water flaxseed

Japanese: tanenanashi, ukikusa

Habit:  aquatic herb

Description:  "Fronds free-floating on water surface, 2-5 cohering in groups connected by elongate, peltately attached stipes, upper surface dark green, lower surface reddish, obovate to orbicular, (3-) 4-8 (-10) mm long, 2-6 mm wide, with 5-11 (-15) conspicuous radiating nerves that crate a peltate appearance, reproducing primarily by asexual budding, over-wintering buds dark brown and reniform, arising from the reproductive pouches and growing nearly to maturity before separating from the parent plant, roots (4) 5-12, fascicled.  Flowers in sac-like spathes open only at apex, with 2 staminate flowers consisting of a solitary anther and 1 pistillate flower consisting of a single ovary with 1-2 ovules.  Fruit slightly winged.  Seed compressed, smooth or slightly reticulate" (Wagner et al., 1999; p. 1458).

Habitat/ecology:  "The species is a weed problem in the world's leading rice-producing countries and a troublesome problem in the world's waterways.  Giant duckweed is most often found in quiet permanent waters.  In mixtures with other duckweeds, it frequents low-lying roadside ditches, sheltered bays, pockets in floating bogs, and sites where town sewage and farm run-off have made waters nutrient rich.  It is often seen in mixtures with larger aquatic species on the vegetation-choked shores of reservoirs, ponds and lakes.  The plant loves full sun but it also frequents woodland and tall grass ponds where there is always partial shade.  Fast water dislodges large populations and aids in the dispersal of the species.  The duckweed will not tolerate salinity.  It can grow in water and on substrates with a wide range of pH"  (Holm et al., 1997; pp. 802, 804).

In Hawai‘i, "naturalized, or possibly indigenous, occurring in taro paddies, slow-running streams, ponds, and marshes" (Wagner et al., 1999; p. 1458).

Propagation:  Primarily by asexual budding (Wagner et al., 1999; p. 1458).

Native range:  "Nearly cosmopolitan, native to Eurasia, Africa, North America and Australia" (Wagner et al., 1999; p. 1458).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Shannon, Robynn K./Herbst, Derral R. (1997) (p. 59) Voucher cited: Stemmermann & Luce 7184 (BISH)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Imada, Clyde T./Staples, George W./Herbst, Derral R. (2000) (p. 12) Voucher cited: C. Imada, W. Char & C. Morden 99-7 (BISH)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, Warren L./Shannon, Robynn K./Herbst, Derral R. (1997) (p. 59) Voucher cited: Degener 8934 (US)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1458) Voucher cited: Forbes 2517.O (BISH)
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	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines Philippine Islands	Philippine Islands	native	Merrill, Elmer D. (1925) (p. 190) Floating on stagnant fresh water at low and medium altitudes.

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		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 802)
Australia Australia (continental)	Australia (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Australia Australia (continental)	Northern Territory		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 802)
Australia Australia (continental)	Queensland		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 802)
Cambodia Cambodia	Cambodia (Kingdom of)		Waterhouse, D. F. (1993) (p. 69)
Central America Central America (Pacific rim)	Costa Rica (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	El Salvador (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Panama (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
China China	China (People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Indonesia Indonesia	Indonesia (Republic of)		Waterhouse, D. F. (1993) (p. 69)
Japan Japan	Japan	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Japan Ryukyu Islands	Ryukyu Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
North Korea North Korea	North Korea (Democratic People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South Korea South Korea	South Korea (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Malaysia Malaysia	Malaysia (country of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Singapore Singapore	Singapore (Republic of)	uncertain if introduced invasive	Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 81) Weed of uncertain origin
South America (Pacific rim) South America (Pacific rim)	Colombia	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South America (Pacific rim) South America (Pacific rim)	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South America (Pacific rim) South America (Pacific rim)	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Taiwan Taiwan Island	Taiwan Island	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Thailand Thailand	Thailand (Kingdom of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Vietnam Vietnam	Vietnam (Socialist Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Canada Canada	Canada	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (continental except west coast) United States (other states)	United States (other states)	introduced cultivated	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (continental except west coast) United States (other states)	United States (other states)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)

Comments:  Reported as possibly an invasive plant in the Hawaiian Islands (Staples et al., 2000).

Control:  If you know of control methods for Spirodela polyrhiza, please let us know.