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. (2011)
Philippines Philippine Islands	Philippine Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
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)	Australia (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Australia Australia (continental)	New South Wales		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 802)
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)
Canada Canada	Canada (country)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
China China	China (People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (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)
El Salvador El Salvador	El Salvador (Republic of)	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)		Waterhouse, D. F. (1993) (p. 69)
Japan Japan	Japan (country)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Japan Ryukyu Islands	Ryukyu Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
North Korea North Korea	North Korea (Democratic People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
South Korea South Korea	South Korea (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Malaysia Malaysia	Malaysia (country of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Nicaragua Nicaragua	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Panama Panama	Panama (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)
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
Taiwan Taiwan	Taiwan Island	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Thailand Thailand	Thailand (Kingdom of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Vietnam Vietnam	Vietnam (Socialist 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)	introduced cultivated	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)
United States (continental except west coast) United States (other states)	United States (other states)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

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

Additional information:
Additional online information about Spirodela polyrhiza is available from the Hawaiian Ecosystems at Risk project (HEAR).

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

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

References:

Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. 2009. A checklist of the total vascular plant flora of Singapore: native, naturalised and cultivated species. Raffles Museum of Biodiversity Research, National University of Singapore. 273 pp.

Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James. 1997. World weeds: natural histories and distribution. John Wiley & Sons. 1129 pp.

Imada, Clyde T./Staples, George W./Herbst, Derral R. 2000. New Hawaiian plant records for 1999. In: Evenhuis, Neal L. and Eldredge, Lucius G., eds. Records of the Hawaii Biological Survey for 1999. Part 1: Articles. Bishop Museum Occasional Papers. 63:9-16.

Merrill, Elmer D. 1925. An enumeration of Philippine flowering plants, vol. 1 [reprint]. Bureau of Printing, Manila. 463 pp.

Staples, George W./Herbst, Derral/Imada, Clyde T. 2000. Survey of invasive or potentially invasive cultivated plants in Hawai‘i. Bishop Museum Occasional Papers No. 65. 35 pp.

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

U.S. Dept. Agr., Nat. Res. Cons. Serv. 2011. The PLANTS Database. National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. 1999. Manual of the flowering plants of Hawaii. Revised edition. Bernice P. Bishop Museum special publication. University of Hawai‘i Press/Bishop Museum Press, Honolulu. 1919 pp. (two volumes).

Wagner, Warren L./Shannon, Robynn K./Herbst, Derral R. 1997. Contributions to the flora of Hawai‘i. In: Evenhuis, Neal L. and Miller, Scott, E., eds. Records of the Hawaii Biological Survey for 1996. Part 1: Articles. Bishop Museum Occasional Papers. 48:51-65.

Waterhouse, D. F. 1993. The major arthropod pests and weeds of agriculture in Southeast Asia. The Australian Centre for International Agricultural Research, Canberra. 141 pp.

Zhengyi, Wu/Raven, Peter H./Deyuan, Hong. 2011. Flora of China (online resource).