Table 3.

Phytogeography and harmful effects of floating aquatic weeds.

Worldwide Distribution	Occurrence	Harmful effects	Sources
1. Azolla pinnata R.Br.
Asia, Tropical America, Tropical Africa and Australia.	Ponds and tanks, deep water rice infestation, lakes, irrigation canals and drainage ditches.	Azolla weevil, Stenopelmus rufinasus, uses the A. pinnata as a host plant, but it is an inferior host and unlikely to support field populations of the weevil. It is possible that thick, complete covering of Azolla can cause de-oxygenation of the water. This can affect organisms such as fish and other aquatic plants. The decay of the plants can lead to a strong odour.	Pemberton and Bodle, 2009; Anonymous, 2010
2. Lemna aequinoctialis Welw. (Syn. L. paucicostata Hegelm.)
Throughout all the warmer regions of both the hemispheres.	Ponds, pools and swamps, natural water bodies for storage.	High intensity invasion lead to fish mortality and decrease in invertebrate diversity, due to invasive nature of Lemma spp.	Lancar and Krake, 2002
3. Lemna gibba Linn.
Europe, S.W. Asia, India, Ceylon, N.E ' S. Africa and S. America.	Natural water bodies for storage, aquatic sports and aesthetic value	High intensity invasion lead to fish mortality and decrease in invertebrate diversity, due to invasive nature of Lemma spp.	Lancar and Krake, 2002
4. Marsilea quadrifoliata Linn.
Cosmopolitan	Pond, ditches, swamps and paddy fields, lakes.	It is regarded as troublesome weed in rice field and irrigation ditches.	Cook et al., 1974
5. Nelumbo nucifera Gaerth. (Syn: Nelumbium nelumbo (L.) Druce, N. speciosum Wild.)
N. temperate zone, Europe and Asia.	Cultivated; wild in Ponds and lakes.	Charm of boating, swimming, bathing and other recreations in water is lost due to infestation of water bodies with such aquatic weeds.	Lancar and Krake, 2002
6. Nymphoides cristata (Roxb.) Ketze. (Syn. Menyanthes cristata Roxb.)
Malaya, China, India and Pakistan	Lakes and tanks growing fishes, irrigation ditches and drainage system.	Causing floods, damages irrigation and drainage systems	Lancar and Krake, 2002
7. Nymphoides indica (L.) Kuntze (Syn: Menyanthes indica L.)
Australia, Cambodia, India, Indonesia, Malaysia, Vietnam; Myanmar, Japan; Korea, Nepal, India Pakistan, SriLanka, Pacific, Islands,	Lakes and tanks growing fishes, irrigation and drainage system.	Causing floods; damages irrigation and drainage systems	Lancar and Krake, 2002
8. Pistia stratiotes Linn.
Pantropical, India, Sri Lanka and Pakistan.	Water-bodies, canals and lakes, irrigation and drainage system. shallow water areas, eutrophied areas.	Influences fishing, power generation, navigation, recreation, waste disposal, water flow problems in irrigation canals	Lancar and Krake, 2002
9. Potamogeton nodosus Poiret
Warmer regions of Europe, N.and Cent. America, Africa and Asia.	Lakes and tanks, water storage reservoirs for city water supply system, fisheries development, irrigation canals and drainage system.	Damaging irrigation canals, and drainage system, ponds, lakes, fisheries areas and rivers	Lancar and Krake, 2002
10. Ricciocapa natans (L.) Corda
Occur nearly worldwide	Shallow water of ponds, pools. Often found growing with duckweeds (Lemna spp., Spirodela sp.)	Fish production is greatly affected by the presence of these weeds. As they cause oxygen depletion, and accumulation of Carbondioxide, gases like hydrogen sulphide and methane are formed; these gases are harmful to the fishes. Decomposing weeds omit offensive odor.	Lancar and Krake, 2002
11. Spirodela polyrrhiza (L.) Schleid.
Tropcal America, Europe, Asia.	Lakes, ponds, marshes and slow streams in areas sheltered from wind.	These aquatic weeds are responsible for lowering quantity as well as quality of water. These weeds cause taste and odour problems and also increase biological oxygen demand because of organic loading.	Lancar and Krake, 2002