duckweed n : any small or minute aquatic plant of the family Lemnaceae that float on or near the surface of shallow ponds

English

Noun

1. Any of several reduced floating aquatic plants in the family Lemnaceae.

Lemnaceae is a family of flowering plants, also known as the duckweed family, as it contains the duckweeds or water lentils. The duckweeds are now known to be a branch of the arum or aroid family (Araceae), so the name 'Lemnaceae' is rapidly falling out of use among botanists.

These plants are very simple, lacking an obvious stem or leaves, but 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 currently holds the record for being the smallest flower in world; measuring in at a size of 0.3 mm long.

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, although in a large pond they 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.

Galicia, Spain

See also

• Lemna
• Spirodela
• Landoltia punctata

• Wolffia

References

• Landolt, E. (1986) Biosystematic investigations in the family of duckweeds (Lemnaceae). Vol. 2. The family of Lemnaceae - A monographic study. Part 1 of the monograph: Morphology; karyology; ecology; geographic distribution; systematic position; nomenclature; descriptions. Veröff. Geobot. Inst., Stiftung Rübel, ETH, Zurich.

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