duckweed

Lemnaoideae
Close up of two different duckweeds: Spirodela polyrrhiza and Wolffia globosa. The very tiny Wolffia plants are under 2 mm long
Scientific classification
Kingdom: Plantae (unranked): Angiosperms (unranked): Monocots Order: Alismatales Family: Araceae Subfamily: Lemnoideae
Genus
Spirodela Landoltia Lemna Wolffiella Wolffia

Lemnaceae is a family of flowering plants, also known as the duckweed family, as it contains the duckweeds or water lentils. Since duckweeds are now considered to be a branch of the arum or aroid family (Araceae), the name 'Lemnaceae' is rapidly falling out of use among taxonomists, who treat it as a subfamily called Lemnoideae.

These plants are very simple, lacking an obvious stem or leaves. They consist of a small 'thalloid' or plate-like structure that floats on or just under the water surface, with or without simple rootlets. The plants have become highly reduced from their relatives in Araceae. Reproduction is mostly by budding, but occasionally a flower consisting of two stamens and a pistil is produced (some view the 'flower' as a pseudanthium, or reduced inflorescence, with three unisexual flowers, derived from the spadix in Araceae). The fruit is a utricle, a sac containing air and a seed designed to float. The flower of the Wolffia is the smallest flower in the world; measuring in at a size of 0.3 mm long.^[1]

Duckweed is an important food source for waterfowl and are eaten by humans in some parts of Southeast Asia (as khai-nam). Some duckweeds are used in freshwater aquariums and ponds where they may spread rapidly and, in a large pond, may be difficult to eradicate once established. The plants can provide nitrate removal (if cropped) and cover for fry. The plants are used as shelter by pond water species, such as bullfrogs and bluegills. The duckweeds are important in the process of bioremediation because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen and phosphates. A cover of duckweeds will reduce evaporation of water compared to a clear surface.

Taxonomy

Classification of the duckweeds in the family Lemnaceae is recognized by most systems of plant classification. It is not recognized by the APG II system, which places the duckweeds in the aroid family the Araceae as subfamily Lemnoideae. The genera of duckweeds are: Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia.

Common duckweed in Galicia, Spain

Lemna minor

Lemna trisulca

Lemna gibba.

Turning the canals of the Poitevin Marsh (Marais Poitevin, France) into the "Green Venice":

Spirodela polyrhiza

Canal green with duckweed

Genomic Sequencing

In July 2008 the US Department of Energy (DOE) Joint Genome Institute announced the Community Sequencing Program will fund the sequencing the genome of the giant duckweed, Spirodela polyrhiza. This will be a priority project for DOE in 2009. The research is intended to facilitate new biomass and bioenergy programs.^[2]

See also

Wikimedia Commons has media related to: Lemnaceae

• Lemna
• Spirodela
• Landoltia punctata
• Wolffia

References

External links

• The Charms of Duckweed by John W. Cross.
• Wayne Armstrong's treatment of the Lemnaceae and allies
• Lemnaceae in Watson, L. and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. Version: 3 May 2006. http://delta-intkey.com
• Duckweed testing in ecotoxicology
• Duckweed
• The Duckweed Genome Project

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