Wolffia arrhiza

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Wolffia arrhiza
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Alismatales
Family: Araceae
Genus: Wolffia
W. arrhiza
Binomial name
Wolffia arrhiza
Detail on the water surface

Wolffia arrhiza is a species of flowering plant known by the common names spotless watermeal and rootless duckweed, belonging to the Araceae, a family rich in water-loving species, such as Arum and Pistia. It is the smallest vascular plant on Earth.[1][2][3] It is native to Europe, Africa, and parts of Asia, and it is present in other parts of the world as a naturalized species.[4][5] It is an aquatic plant which grows in quiet water bodies such as ponds. The green part of the plant, the frond, is a sphere measuring about 1 mm wide, but with a flat top that floats at the water's surface. It has a few parallel rows of stomata.[2] There is no root. The plant produces a minute flower fully equipped with one stamen and one pistil. It often multiplies by vegetative reproduction, however, with the rounded part budding off into a new individual.[2][6] In cooler conditions the plant becomes dormant and sinks to the bed of the water body to overwinter as a turion.[7] The plant is a mixotroph which can produce its own energy by photosynthesis or absorb it from the environment in the form of dissolved carbon.[3]

This tiny plant is a nutritious food. Its green part is about 40% protein by dry weight and its turion is about 40% starch.[8][9] It contains many amino acids important to the human diet, relatively large amounts of dietary minerals and trace elements such as calcium, magnesium, and zinc, and vitamin B12.[9] It has long been used as a cheap food source in Myanmar, Laos, and Thailand, where it is known as khai-nam ("eggs of the water").[10] The plant is prolific in its reproduction, growing in floating mats that can be harvested every 3 to 4 days; it has been shown to double its population in less than four days in vitro.[11]

It is also useful as a form of agricultural and municipal water treatment.[12] It is placed in effluent from black tiger shrimp farms to absorb and metabolize pollutants.[13] The plants grow quickly and take up large amounts of nitrogen and phosphorus from the water.[8] The plants that grow in the wastewater can then be used as feed for animals, such as carp,[14] Nile tilapia,[15] and chickens.[7]


  1. ^ Pietryczuk, A., et al. (2009). The effect of sodium amidotrizoate on the growth and metabolism of Wolffia arrhiza (L.) Wimm. Polish Journal of Environmental Studies 18:5 885-91.
  2. ^ a b c Pan, S. and S. S. C. Chen. (1979). The morphology of Wolffia arrhiza: A scanning electron microscopic study. Bot Bull Academia Sinica 20 89-95.
  3. ^ a b Czerpak, R., et al. (2004). Biochemical activity of auxins in dependence of their structures in Wolffia arrhiza (L.) Wimm. Acta Societatis Botanicorum Poloniae 73:4 269-75.
  4. ^ "Wolffia arrhiza". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2 January 2018.
  5. ^ "Wolffia arrhiza in Flora of North America @ efloras.org". efloras.org.
  6. ^ MoBot: Wolffia arrhiza
  7. ^ a b Al Khateeb, N. Duckweed use for sewage treatment and fodder production in Palestine. Water & Environmental Development Organization, Palestine.
  8. ^ a b Fujita, M., et al. (1999). Nutrient removal and starch production through cultivation of Wolffia arrhiza. Journal of Bioscience and Bioengineering 87:2 194-8.
  9. ^ a b Czerpak, R. and I. K. Szamrej. (2003). The effect of β-estradiol and corticosteroids on chlorophylls and carotenoids content in Wolffia arrhiza (L.) Wimm. (Lemnaceae) growing in municipal Bialystok tap water. Polish Journal of Environmental Studies 12:6 677-84.
  10. ^ Bhanthumnavin, K. and M. G. McGarry. (1971). Wolffia arrhiza as a possible source of inexpensive protein. Nature (letter) 232:495.
  11. ^ National Academy of Sciences. Making aquatic weeds useful: Some perspectives for developing countries. 1976. Page 149.
  12. ^ Körner, S., et al. (2003). The capacity of duckweed to treat wastewater. Journal of Environmental Quality 32:5 1583-90.
  13. ^ Suppadit, T., et al. (2008). Treatment of effluent from shrimp farms using watermeal (Wolffia arrhiza). ScienceAsia 134 163-8.
  14. ^ Naskar, K., et al. (1986). Yield of Wolffia arrhiza (L.) Horkel ex Wimmer from cement cisterns with different sewage concentrations, and its efficacy as a carp feed. Aquaculture 51:3-4 211-16.
  15. ^ Chareontesprasit, N. and W. Jiwayam. (2001). ##An evaluation of Wolffia meal (Wolffia arrhiza) in replacing soybean meal in some formulated rations of Nile tilapia. Pakistan Journal of Biological Sciences 4:5 618-20.

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