Duckweeds are the smallest of the flowering plants, which consist of tiny, green, rounded, leaflike bodies (fronds) that float on the water’s surface. Each duckweed plant (genus Lemna) is a green, leaflike circular or oval frond less than 1/4 inch across, each bearing a single short, hairlike root that dangles into the water. Giant duckweeds grow in clusters of 1-3, with 2-20 roots per frond.
And this is “Kudhu fai jawaahiru”
Compare the texture with the duckweeds. Is there any difference in appearance?
Fronds measure to nearly 3/8 inch across, depending on genus.
Habitat and conservation:
Duckweed mainly grows in warm, wet environments around the world, either in shade or direct sunlight. It floats, forming a blanket over small bodies of slow-moving water. These bodies of water contain high levels of nutrients such as phosphorus or nitrogen. Most duckweeds float on the surface of shallow and stagnant ponds, lakes, ditches, swamps, and still backwaters of streams and rivers. They sometimes form mats and can be stranded on mud by a receding waterline. One species, star duckweed (L. trisulca), grows submerged in cool, flowing water of spring branches and streams. In ponds, common duckweeds (notably L. minor) can spread quickly, especially when nutrients such as nitrogen and phosphorus are plentiful, and become a nuisance.
By providing food and cover for many types of aquatic wildlife, duckweed contributes to fishing, frog and duck hunting, and more. In old, nutrient-rich ponds, and those contaminated with feedlot runoff or sewage, duckweed can spread quickly, cover the surface, and become a nuisance.
Duckweed and watermeal are important foods for wildlife, especially waterfowl. They also provide cover for frogs, turtles, and more. In the presence of excessive nutrients, dense duckweed growth can block out sunlight, shading out oxygen-producing plants below, upsetting a pond’s natural balance.
Depending on strain and growing conditions, duckweeds can have very high protein content of up to 50% of dry mass. High levels of vitamins are also present. The taste is remotely similar to spinach. Duckweeds have historically played a role in some east Asian cuisines (Wolffia genus). Because of rapid growth and ease of cultivation, duckweeds for consumption by animals and humans are now getting more attention. Current uses as animal fodder are mostly as fish food (carp, tilapia) and bird food (chicken, duck). Possible uses as part of a human diet are still vastly under-explored.
It is edible and has a unique flavor that compliments numerous dishes. Locating duckweed may be difficult, but many farmers markets in rural areas sell duckweed, and it can be ordered through specialty gourmet outlets in some areas.
Duckweed is a source of food for water fowl and even people in parts of Southeast Asia such as Thailand. It also provides shelter for pond animals, such as bullfrogs. It can be placed in freshwater aquariums.
Duckweed can multiply at an incredibly fast rate. It can cover the surface of a body of water, blocking sunlight and killing fish and aquatic plant life. This growth also can clog outlets such as water drains.Using herbicides to kill an overgrowth of duckweed is ineffective because duckweed thrives on the nutrients in the water. To control the growth of duckweed, reduce the flow of nutrients into the water or remove the duckweed at repeated intervals.
Duckweed can be used to help purify water by controlling algae growth and converting waste and sewage water into treated water and biomass (duckweed leaves and roots). However, it can’t process toxic substances such as heavy metals and pesticides.Duckweed also reduces water evaporation and keeps water cool.
Duckweed in various environments
Duckweed is an important high-protein food source for waterfowl and also is eaten by humans in some parts of Southeast Asia (as khai-nam). Sometimes it is cited as an overlooked source for application as a food for a hungry world that produces more protein than soybeans.
Some duckweeds are introduced into freshwater aquariums and ponds where they may spread rapidly. This introduction may be deliberate or unintended and once established in a large pond, may be difficult to eradicate. Occurring naturally by being carried on the feathers, shells, and coats of native species, the plant is introduced readily by birds, turtles, reptiles, and aquatic mammals visiting multiple ponds, rivers, and lakes. In water bodies with constant currents or overflow, the plants are carried down the water channels and do not proliferate greatly. In some locations a cyclical pattern driven by weather patterns exists in which the plants proliferate greatly during low water flow periods, yet are carried away as rainy periods ensue.
The tiny plants provide cover for fry of many aquatic species. The plants are used as shelter by pond water species such as bullfrogs and bluegills. They also provide shade and, although frequently confused with them, can reduce certain light-generated growths of photoautotrophic algae.
The plants can provide nitrate removal, if cropped, and the duckweeds are important in the process of bioremediation because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen and phosphates. For these reasons they are touted as water purifiers of untapped value.
The Swiss Department of Water and Sanitation in Developing Countries, SANDEC, associated with the Swiss Federal Institute for Environmental Science and Technology, asserts that as well as the food and agricultural values, duckweed also may be used for waste water treatment to capture toxins and for odor control, and, that if a mat of duckweed is maintained during harvesting for removal of the toxins captured thereby, it prevents the development of algae and controls the breeding of mosquitoes. The same publication provides an extensive list of references for many duckweed-related topics.
These plants also may play a role in conservation of water because a cover of duckweed will reduce evaporation of water when compared to the rate of a similar size water body with a clear surface.
The duckweeds long have been a taxonomic mystery, and usually have been considered to be their own family, Lemnaceae. They primarily reproduce asexually. Flowers, if present at all, are small. Roots are either very much reduced, or absent entirely. They were suspected of being related to the Araceae as long ago as 1876, but until the advent of molecular phylogenyit was difficult to test this hypothesis. Starting in 1995 studies began to confirm their placement in the Araceae and since then, most systematists consider them to be part of that family.
Their position within their family has been slightly less clear, but several twenty-first century studies place them in the position shown below. They are not closely related to Pistia, however, which also is an aquatic plant in the family Araceae.
The genera of duckweeds are: Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia.
In July 2008 the U.S. Department of Energy (DOE) Joint Genome Institute announced that the Community Sequencing Program would fund the sequencing the genome of the giant duckweed, Spirodela polyrhiza. This was a priority project for DOE in 2009. The research is intended to facilitate new biomass and bio-energy programs.
Duckweed is being studied by researchers around the world as a possible source of clean energy. In the United States, in addition to being the subject of study by the DOE, bothRutgers University and North Carolina State University have ongoing projects to determine if duckweed might be a source of cost-effective, clean, renewable energy. Duckweed is a good candidate as a biofuel because as a biomass it grows rapidly, has 5 to 6 times as much starch as corn, and does not contribute to global warming. Duckweed is considered a carbon neutral energy source, because unlike most fuels, it actually removes carbon dioxide from the atmosphere.
Duckweed also functions as a bioremediator by effectively filtering contaminants such as bacteria, nitrogen, phosphates, and other nutrients from naturally occurring bodies of water, constructed wetlands and waste water. One study in Australia surrounding aquaculture suggests that although duckweed is initially effective as a nutrient filter, over time some nutrient build-up returns.
Duckweed is the world’s smallest flowering plant. Roughly 40 species of duckweed exist and grow worldwide; these very small aquatic plants grow so rapidly that a single floating colony can double in size in less than 48 hours. Duckweed grows best in temperate and tropical climates, and prefers areas with little wave or wake, where it is sheltered from the wind; though it has also been found in areas with extreme temperatures and growing conditions. Duckweed plants remove a very high percentage of nutrients from the water during their growth cycle, and so are potentially valuable both as a food source and as a water purification system.
Fresh duckweed is between 90 and 95 percent water; this is not surprising since it is an aquatic mass with a low enough density to float. To measure its other nutritional values, scientists look at its dry mass.
Duckweed has gained the attention of agricultural specialists interested in its potential as a feed supplement for livestock because of its high protein value. Duckweed grown in cultivated conditions can contain up to 45 percent crude protein in its dry mass. The chemical makeup of these proteins, rich in the essential amino acids lysine and methionine, make it compositionally more like an animal protein than a vegetable protein.
The plant as it naturally occurs typically has a fiber content of between 15 and 30 percent. In ideal water conditions however, duckweed can be cultivated with as little as 5 percent fiber in its nutritional composition. As growth conditions improve and the fiber mass is minimized, the total amount of protein in the plant is maximized.
Other Nutritional Elements
The dry mass of duckweed, when tested, contained between 1.8 and 9.2 percent lipid tissue, and between 14.1 and 43.6 percent carbohydrates. Cultured duckweed, specifically, has demonstrated larger concentrations of certain trace minerals and pigments, like beta carotene and xanthophyll, nitrogen and phosphorus.
Because of its rapid growth and its nutritional composition, duckweed is being studied as a potential food source for poultry, hog, cattle, and human consumption. The fiber content of popular feed grains like soy and milo can be as high as 50 percent, which is not readably digestible. Duckweed, as a feed source, could be broken down and more completely consumed by the animal, increasing feed conversion rates. Also, the whole duckweed plant can be used as feed, saving the processing expenses and plant waste associated with feeding grain. In terms of dry mass grown per acre, duckweed could be grown on 10 percent of the space required to produce a similar amount of soybeans, and would only require 20 percent of the space required to grow the equivalent amount of corn.
Duckweed for Bio-energy
Duckweed produces biomass faster than any other flowering plant. It has clear potential as an alternative for biofuel production.
Duckweed as Biosensors
Duckweeds are used for the detection of heavy metals and organic contaminants. A variety parameters can then be measured to assess the health of the plants: growth rate, leaf size and color, root size etc.
Duckweed for Contaminant Removal
Duckweed is very efficient at cleaning water. First it will remove all macronutrients. Then it will remove micronutrients. Finally it will remove all metal ions, including toxics and radioactives. As such, it can be used to ‘polish’ industrial effluent, pre-treat sewage, denitrify effluent from other aquaculture activites and other nitrogen drainange situations (stock lots, etc.).