Fostering Duckweed

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Baggenstos/Rudolf (Heidy Baggenstos & Andreas Rudolf) are an Art-Collective and have worked with duckweed for several pieces of art.
On this webpage, we publish a summary of all the research underlying the art project and other things we have done, even if they have not directly fed into a piece.
Recognizing the fast growth of a plant in our aquarium triggered our interest. This plant was duckweed. Duckweed is very common and also a native plant in Switzerland. We thus started cultivating duckweed that we had found in ponds close to where we live and wondered what nutrients they might need and how we could provide them. It turned out that it is possible to produce the required nutrients ourselves in a Do It Yourself manner by using our own organic wastes.
Because duckweed is edible we started food experiments and processed the duckweed in a variety of manners.
More and more we got into a closed cycle between the plant and us and established a human-plant ecosystem.

Duckweed in Switzerland is listed on the red list of endangered species. Depending on the type of species, their degree of endangerment is different. In 2017, we started multiplying Lemna gibba, a species that is locally extinct in Switzerland.
What can we do with its taste? Does a species that is almost extinct taste differently from other duckweed species?

The great promises

Duckweed might be the food of the future?
Grown under ideal conditions, duckweed ranges between 25% and 45% protein and doubles its growth every 36 hours. Duckweed produces biomass faster than any other flowering plant. This tiny aquatic plant has tremendous potential for cleaning up pollution, combating global warming and feeding the world. (this is a very optimistic view I have to say)

Bioful: It has potential as an alternative for biofuel production. (Methanol und Ethanol)
Bioremediation: Living Machines for cleaning wastewater.
Biomining: of phosphorus and other minerals/nutrients from wastewater.
Bio-sensors: Duckweeds are used for the detection of heavy metals and organic contaminants.
Animal food: food for fish (tilapia), chickens, pigs and of course ducks! Duckweed integrates very nicely into aquaponics. It can provide all the protein needs for some breeds.
Human food: Depending on strain and growing conditions, duckweeds can have very high protein content of up to 50% of dry mass.
In Space: food production in bioregenerative life support systems in space.
--> source

Features of Duckweed

- Duckweed are the fastest growing higher plants in the world.
--> source: Enzyklopädie Essbare Wildpflanzen 2013 Steffen Guido Fleischhauer / Jürgen Guthmann / Roland Spiegelberger -- and -->here

- Duckweed belong to the smallest flowering plants in the world and spread primarily by vegetative growth. Daughter fronds bud from reproductive pockets on the side of a mature frond. An individual frond may produce as many as 10 generations of progeny over a period of 10 days to several weeks before dying. As the frond ages its fiber and mineral content increases, and it reproduces at a slower rate.

- In fall, they decay and completely disappear from the surface. Beforehand the plant produces small buds, sinking to the bottom and overwintering.
--> source: Swiss Plant Life / Ewald Weber 2009

- Die Wasserlinse existiert unter Wasser und steigt zur explosionsartigen Vermehrung an die Wasseroberfläche auf. Sie stellt damit ein Wesen der mystischen „Anderswelt“ dar, des Reiches der Ahnen und Geister.
- Eine Wasserfläche von 10m2 deckt den Proteinbedarf eines Menschen, selbst wenn der Umweg über Nutzvieh gewählt wird.
- Inhaltsstoffe: Calcium, Carotinoide, Flavonoide, Fette, Magnesium, Oxalate, Phosphor, Proteine mit allen essentiellen Aminosäuren, Schleimstoffe, Spurenelemente, Vitamine und Xanthophyll.
--> source: Wilde Genüsse / Margot Fischer 2014

- Compared with most plants, duckweed fronds have little fiber -- as little as 5 percent in cultured plants -- because they do not need structural tissue to support leaves or stems. As a result virtually all tissue is metabolically active and useful as a feed or food product.
--> source

- Duckweed protein has higher concentrations of the essential amino acids, lysine and methionine, than most plant proteins and more closely resembles animal protein in that respect. Figure 3 compares the lysine and methionine concentrations of proteins from several sources with the FAO standard recommended for human nutrition.
The protein content of duckweed is compared with several animal feed ingredients in Figure 5

- Cultured duckweed also has high concentrations of trace minerals and pigments, particularly beta carotene and xanthophyll, that make duckweed meal an especially valuable supplement for poultry and other animal feeds. The total content of carotenoids in duckweed meal is 10 times higher than that in terrestrial plants;
--> source

Wasserlinsen haben biologische Eigenschaften, die sie für die Reinigung von Gewässern interessant machen und ist darum auch Gegenstand von Forschungsprojekten.
- Ihr Wachstum ist auch unter lichtschwachen bis fast lichtlosen Verhältnissen möglich.
- Sind mixotroph und können einen Teil ihre Energie aus organischen Stoffen gewinnen.
- Stomata sind immer offen -­‐> keine Photorespiration, was eine Energieersparnis für die Pflanze darstellt.
- Unter günstigen Bedingungen sehr schnelles Wachstum (0,7 Tage pro Generation)
- Sind als schwimmende Pflanzen an der Grenzphase zwischen Wasser und Luft nicht auf aerobe Verhältnisse im Wasser angewiesen.
- Werden mit Verschiedenen Schmutz- und Schadstoffen fertig, u.a. auch mit Mikroverunreinigungen
--> source: Andreas Schönborn

- Sie sind in der Lage Schwermetalle aufzunehmen.
- Im Pflanzenbestimmungsbuch von Peter M. Kammer ist erwähnt, dass Lemna Minor L. eine hohe Aufnahme- und Speicherkapazität für Radium, Jod und Brom besitzen.
--> source: Pflanzen einfach bestimmen / Peter M. Kammer 2016


Family: Araceae
Subfamily: Lemnoideae
Lemnaceae: Lemna minor
  Lemna trisulca
  Lemna gibba
  etc. (A total of 13 spp.)
Landoltia: Landoltia Punctata
Spirodela: Spirodela polyrrhiza
  Spirodela intermedia
  Spirodela biperforata
Wolffia: 11 spp.
Wolffiella: 10 spp.

Trivial names:
Duckweed, water lentils (E)
Entengrütze, Entenflott, Entengrün, Wasserlinsen (D)
Chrottechröös, Chrottehuus, Äntegriitze (CH)

--> Species Of Lemnaceae In Western North America
--> Naturhistorisches Museum Wien „BOTANIK IM BILD“ - Wasserlinsengewächse
--> RDSC Rutgers Duckweed Stock Cooperative - What is the true number of duckweed species?
--> USDA United States Departement of Agriculture - Natural Resources Conservation Service
--> Landolt Duckweed Collection Zurich

Duckweed on the RED list

Duckweed is different endangered by region. In some regions they are not endangered, in some they are already extinct.

Spirodela polyrrhiza Mittelland - Potenziell gefährdet
  Alpensüdflanke - Regional ausgestorben
Lemna gibba L. Mittelland (MP) - Regional ausgestorben (RE)
Lemna trisulca L. Mittelland - Potenziell gefährdet
  Westliche Zentralalpen (WA) - Stark gefährdet (EN)
Lemna minuta Mittelland (MP) - Stark gefährdet (EN)
  Alpensüdflanke - Stark gefährdet (EN)

For more Details see the site of Info Flora: Das Nationale Daten- und Informationszentrum der Schweizer Flora

Red list of vascular plants in Switzerland 2016

Red list of endangered species in Switzerland: ferns and flowering plants Bundesamt für Umwelt BAFU 2002

Starting with experimentations

Heidy once get some duckweed in an aquarium store for her fish aquarium. They usually dont sell duckweed, it was for free. Since then, the duckweed overgrows the aquarium constantly. Instead of throwing a quarter of them away once a week, we could make something out of it.

L.gibba culture on the balcony of Andreas 2017
We started with an aquarium the size of 40 x 50 x 40cm with a pump for water circulation (without Filter) and air supply Adult and baby water lentil Siede view Backside view Under backlight 50g fresh duckweed from the aquarium Onions, duckweed and Chilli roasted in the pan. We used here way too much chilli, it got really hot Surprisingly, the nice green color stayed and didn‘t change much during cooking 2,5 g dried duckweed in a petridish Early trials of duckweed-chips First try of duckweed crisps Two Lemnaceae buds, found in early April 2016 on a pond surface. (Frontside) Two Lemnaceae buds. (Backside) Duckweed from a pond near Paul Scherrer Institut PSI Villigen Switzerland Duckweed cultures on the balcony of Andreas 11.5.2016 Duckweed cultures of various species on the balcony of Heidi 1.6.2016 Duckweed cultures on the balcony of Andreas 11.5.2016 Spirodela polyrrhiza (on the right) can become „very big“ compared to Lemna minor (left) Urinlabor at Eawag - Swiss Federal Institute of Aquatic Science Facilities for the nitrification process at EAWAG Dübendorf Pond in Stäfa at 19. Dec. 2016 - No water lentils are visible at the surface anymore Our Lemna minor culture at the studio. Outside it‘s snowing. 10.1.2017 Lemna gibba L.gibba - With only a few pieces we began to cultivate the L.gibba specie in sterile bottles L.gibba - They multiplied quite well and become more and more L.gibba - After two months we could expand to bigger containers L.gibba starter culture at Andreas home L.gibba culture on the balcony of Andreas 2017 L.gibba starting culture at Stadionbrache 2017 L.gibba culture at Stadionbrache summer 2017 If the water surface is densely covered, it carries thirsty insects Cheese making with duckweed flavour fresh cheese with Lemna minor Fresh cheese from 4l milk when draining Cheese salting Cheese during ripening, stored at 15 degree celsius Salt water with spices (dried duckweed) for the daily cheese care Lemna minor cheese becomes purple after a few days. Unfortunately the color vanishes after a few days. Unfortunately, the color doesn't last very long. Cheese after 10 days ripening time Duckweed-Cheese (Lemna. minor flavour / Spirodela polyrrhiza flavour) «Nahreisen 2017 - Kreisläufe & Energieflüsse» Presentation at Stadionbrache Zürich, 25.5.2017 The presentation was followed by a degustation We cooked duckweed vegetables «Nahreisen 2017 - Kreisläufe & Energieflüsse» Presentation and degustation at Stadionbrache Zürich, 5.6.2017 Curious visitors taste our duckweed kitchen Display with our cheese, liqueur and baked goods made of duckweed

Duckweed ponds we found in pure nature

Small pond with duckweed in a garden, Zurich Wiedikon Friesenbergstrasse 94. June 2016.
Small pond with a few duckweed in early April 2016 Small pond with duckweed in a garden, Zurich Wiedikon Friesenbergstrasse 94. June 2016. Duckweed in Pardubice (Czech Republic) Photography by Stefan Ineichen ( Duckweed at Rheinufer Haltingen D. Photography: Daniel Marti 2016. Duckweed in Central Park New York. Photography: Stefan Ineichen 2016. Duckweed in Rotterdam. Photography: Stefan Ineichen 2016. Pond with Lemna trisulca in Rüschlikon ZH. June 2016. Pond in Rüschlikon ZH with another Lemna species. June 2016. 6.8.2016 Bornhöved D Pond in Stäfa ZH all over covered with mainly Spirodela polyrrhiza. August 2016. One of some small ponds near PSI Villigen Switzerland with mainly Spirodela polyrrhiza. 3.10.2016 One of some small ponds near PSI Villigen Switzerland with mainly Spirodela polyrrhiza. 3.10.2016 A bigger pond with Lemna trisulca. Near PSI Villigen Switzerland 3.10.2016 Pond in Stäfa at 19. Dec. 2016 - No water lentils are visible at the surface anymore. Klingnauer Stausee summer 2017 Koblenz CH summer 2017 Two kinds of water lentils in a pond (Koblenz CH 2017) Leuggern summer 2017 Fulda, Kassel summer 2017

What we are interested in

- Lemnas sind geniessbar und verfügen über einen eigenen, etwas teichigen Geschmack. Zudem, und dafür werden sie allerseits gepriesen, enthalten sie viele Proteine und alle essentiellen Aminosäuren.
--> Wilde Genüsse / Margot Fischer 2014

- Wasserlinsen gedeihen offensichtlich gut in überdüngten Gewässern und sind sogar auf Klärbecken zu finden.
- Duckweeds grow under a wide variety of conditions, they are generally not found in oligotrophic water (water in which nutrients are in low supply). Exceptions are waters heavily contaminated by waste water.
--> source

Nutrients from urine and organic wastes
- Nutrients for duckweed can come from fertilizer or organic wastes.
--> source
- Nutrients for duckweed may be supplied from sources such as cattle dung, pig waste, human urine, biogas plant slurry, leachate from silage or compost or other organic matter in slurry form.
--> source
The same is also mentioned in the article „Duckweed Aquaculture“ Growth conditions: The natural habitat of duckweed is floating freely on the surface of fresh or brackish water sheltered from wind and wave action by surrounding vegetation. The most favorable circumstance is water with decaying organic material to provide duckweed with a steady supply of growth nutrients and trace elements.
--> source
To cultivate duckweed a farmer needs to organize and maintain conditions that mimic the natural environmental niche of duckweed: a sheltered, pond-like culture plot and a constant supply of water and nutrients from organic or mineral fertilizers. Wastewater effluent rich in organic material is a particularly valuable asset for cultivating duckweed because it provides a steady supply of essential nutrients and water.
--> source

Urine as nutrient source
What we want to do is, to produce nutrients from own urine and kitchen waste for duckweed.
First we thought to make a transformation of urine into nitrate, called nitrification. Nitrification is caused by nitrifying bacterias. Urea is hydrolysed into ammonium (NH4+) by bacteria containing an enzyme called urease. Ammonium is transformed by a type of bacteria into Nitrite (NO2-), and in a further step Nitrite is transformed by another class of bacteria into nitrate (NO3).
--> See a project on the webpage of Hackuarium: From urine to nitrate
--> see also: Nitrification
--> See the VUNA project: Nutrient recovery from urine VUNA – Nährstoffrückgewinnung aus Urin (Eawag - Swiss Federal Institute of Aquatic Science, Bastian Etter)

But, one of the main nutriens of duckweed is ammonium ion NH4+ (Nitrogen). Besides, human urine contains also phosphorus. It‘s not at all necessary to make nitrate first. You can fertilize the plants with urine directly.
In spring we could meet Bastian Etter (He works on the VUNA project) at EAWAG and we talked about the nutriens in urine. Bastian Etter recommended us to fertilize duckweed with urine directly. Its not necessary to process urine if it doesn‘t contain residuals of drugs. So far as we produce urine by yourself we can ensure that no drugs are contained.
So, we can produce the nutrients by yourself.

Art / Design / Products using Duckweed

- 431art (Haike Rausch and Torsten Grosch)

431art "Lemna Minor squares" 431art "lemna minor laboratory 02" Adriana Stadler "Wasserträger" Katharinen St.Gallen 2007 Baggenstos/Rudolf "Fostering Duckweed - From urine to protein" 2016 Ken Rinaldo & Amy M. Youngs "Farm Fountain" 2007 Duckweed serves in this project as fish food.

Market oriented production

A company in Florida grows Lemnoideae plant to produce proteins for several products. It‘s known under the name: LENTEIN TM Plus POWDER

--> source

--> On its website, they praise the very good nutrition facts of their duckweed powder.

--> There are also to find datas about comparisons with Soy, Whey, Pea or Chlorella and Spirulina (of course, always in comparison of their powder product)

Remark to the calcium oxalate of duckweed

Calcium oxalates are often not really mentioned in recipes or texts about duckweed. We think this is because the amount of calcium oxalate in duckweed depends greatly on the calcium content of the water on which they are growing, and how they are prepared for food. But it‘s worth to consider the fact that duckweed belong to the family of the Araceae, and they are toxic.

Calcium oxalate is not a nutrient (nor a beneficial source of calcium), and it can be toxic in large doses.  Duckweeds can contain up to 2 — 4 percent oxalic acid equivalents by weight.  However, oxalate also is found in a great many leafy and very nutritious vegetables, including spinach, swiss chard and others. Elevated calcium in the water favors formation of calcium oxalate crystals. Their content can be lowered by growth on low-calcium medium.
Dry heat has been used to break down calcium oxalate in other foods. Cooking — boiling or roasting — would also kill any bacteria et cetera on or in the duckweed. Some suggest, to boil the duckweed, change water and then blend it.
--> Eat The Weeds and other things, too

Die Giftigkeit vieler Aronstabgewächse ist vom Verhältnis der in der Pflanze vorkommenden gelösten Oxalate zu den als Raphiden verfestigten abhängig.
Oxalsäure an sich ist in heissem Wasser einigermassen gut löslich. Das heisst, dass wir einen Bestandteil der giftigen Stoffe durch Kochen stark verdünnen können. Ausserdem besteht die Gefahr der Raphiden darin, dass sie oft in Zellen vorliegen, die unter Druck stehen. Ausgelöst können diese Zellen die Nadeln wie kleine Pfeile in die Schleimhaut von Rachen und Magen stossen. Durch den Kochvorgang wird dieser Überdruck aufgelöst, so dass nach längerem Erhitzen keine Vergiftungserscheinungen mehr zu erwarten sind. In grösseren Mengen sollten Wasserlinsen nur prozessiert zu sich genommen werden. Am besten zu Brei kochen.
Calcium oxalate crystals (raphides) like double-pointed needles.
—> Pflanzliche Notnahrung : Survivalwissen für Extremsituationen Johannes Vogel 2014

Oxalsäure ist die einfachste Dicarbonsäure und recht gut in Wasser löslich. Oxalsäure ist in höherer Konzentration giftig. Die wasserlöslichen Natrium-, Kalium-, und Ammoniumsalze wirken ätzend auf die Schleimhäute des Magen-Darm-Traktes, wodurch sie eine starke Reizwirkung ausüben. Oxalsäure kommt in vielen essbaren Wildpflanzen vor. Man findet die Verbindung in höheren Konzentrationen auch in vielen gängigen Nahrungsmitteln wie Mangold, Spinat und Roten Rüben. Geringe Konzentrationen sind in vielen Lebensmitteln wie Tomaten, Tee (insbesondere schwarzer Tee und Pfefferminztee), Kakao und sogar in Schokolade zu finden.
--> Enzyklopädie Essbare Wildpflanzen 2013 Steffen Guido Fleischhauer / Jürgen Guthmann / Roland Spiegelberger

Landolt Duckweed Collection

The Landolt Duckweed Collection contains samples of every known species of duckweed in the world.
The purpose oft the collection is to preserve these species in order to provide living samples available for research and also to provide a forum for the exchange of information.
The duckweed collection is located at Spiegelgasse 12 in Zurich.


- Wasserlinsenelixier nach Hildegard von Bingen -- and -->here
- Wasserlinsenpüree
- Wolffia Aziza im Quark
- Wolffia Used For Nutritious Gourmet Dishes

Im Buch Köstliches von Sumpf- und Wasserpflanzen von Dr. Markus Strauss, 2013 sind einige Rezepte zu finden:
- Sommerliche Gazpacho aus Roter Bete und Wasserlinsen
- Klare Gemüsebrühe mit Wasserlinsen
- Indisches Linsengericht mit dreierlei Linsen
- Würzige Linsensauce zu Nudeln

Ein Rezept-Tipp von S.66: Wasserlinsen sind auch in roher Form lecker. Man kann sie wie Sprossen verwenden: Als Beimischung in Salaten, Dips, und Brotaufstrichen. Auch zum Garnieren von belegten Broten, Salaten und Gemüsegerichten sehen sie apart und aussergewöhnlich aus.
Webseite von Dr. Markus Strauss

Zu finden in: Wilde Genüsse - Das Kochbuch Margot Fischer 2014

Further Links

There is a vast amount of scientific research and available information on the Internet about duckweed.
Here a selection of useful links:

- Synthetic Media for Growing Duckweeds
- The Charms of Duckweed
- Lemnaceae species:
- A More detailed list of the Lemnaceae species:
- Eat the weeds / Foraging with Green Deane, A useful article about duckweed
- Open Source Ecology
- LemnaPedia
- LemnaTec Literature
- ILA - International Lemna Association
- RDSC - Rutgers Duckweed Stock Cooperative State University of New Jersey. (A duckweed collection available for researchers)