Duckweed
Lemna minor
Botanical family: Araceae (formerly Lemnaceae)
A small floating plant: each oval frond, a few millimetres long, bears a single root, and the fronds often stay attached in small groups before forming a mat (DORIS, FFESSM). Duckweeds are rich in protein, about 20 to 35 % of dry matter depending on the species, with an amino-acid profile close to WHO recommendations (Appenroth et al., 2017, Food Chemistry). Active vitamin B12 was measured in a cultivated strain of a related species, Wolffia globosa (Mankai, Sela et al., 2020, Nutrients); this result does not extend to pond duckweed. A neutral, slightly crunchy taste, close to very young cress. Traditional Asian preparations: soups, omelettes, curries.
Sun to partial shade
Still water rich in nitrogen, 18-30 °C during growth
Floating plant, permanent water
Overwinters dormant at the surface (temperate climate)
Very rare, almost exclusively vegetative propagation (doubling in 24-48 h)
Role in permaculture
A floating water cover that takes up the pond's nitrogen and phosphorus; grown in clean water, it is a protein-rich food, rediscovered in the West by Wageningen research since 2015 as a protein of the future. To be harvested with a net as soon as the surface is a third covered.
Good companions
Provide shade or shelter
Traditional companion planting (benefit not demonstrated)
Poor companions
Invasive species: smother the habitat
Seasons & availability
Increased vegetatively, it carpets the surface of still water from spring to autumn, then overwinters on the bottom as dormant buds, the turions, which rise again in spring when the water warms.
Available: April, May, June, July, August, September, October.
Guidance for the oceanic / temperate climate; it may vary with your region, altitude, exposure and growing method.
Sources
- Plants For A Future, « Lemna minor » (pfaf.org/user/Plant.aspx?LatinName=Lemna+minor)
- Missouri Botanical Garden, « Lemna minor » (plantfinder.mobot.org/PlantFinderDetails.aspx?taxonid=281696)
Nutritional & medicinal properties
For educational purposes. Not a substitute for medical advice. Effects depend on the form, the dose and personal context.
Precautions & contraindications
Like cattail, it can concentrate water pollutants, and its fast growth makes it a purifying plant: no harvesting for food outside controlled water. Its fronds can thus become loaded with heavy metals; for PFAS ('forever pollutants'), a laboratory study showed this for a single compound, PFOA (Noori et al., 2025, Frontiers in Plant Science 15:1493896, DOI 10.3389/fpls.2024.1493896): the plant CONCENTRATES this pollutant in its fronds and roots rather than removing it. A duckweed grown in contaminated water is therefore itself loaded: as a precaution, do not eat it or give it to animals. These compounds are also found in rainwater: according to Cousins et al. (2022, Environmental Science & Technology), PFOA levels there exceed US drinking-water health advisories even in remote regions, and PFOS levels often exceed them. A food harvest is therefore only conceivable in a dedicated basin, fed with rainwater, with controlled inputs, in a rural area and away from areas of high atmospheric pollution (dense urban, major road axes, intensive agriculture upstream): see the concept 'Rainwater quality'. The EFSA has moreover flagged, for consumption, a possible overexposure to manganese and a potential allergen linked to the high protein content. Never confuse it with the aquatic fern Azolla filiculoides, common in the same biotopes, which hosts a symbiotic cyanobacterium (Anabaena/Nostoc azollae): as a precaution, do NOT eat azolla, as some cyanobacteria produce cyanotoxins (hepatotoxic microcystins, neurotoxic anatoxins). For any regular food use, seek the advice of a professional.
Species & varieties
The best-known species and varieties in France.
Species
Voices of peoples
Paraphrases attributed to their documented sources. Never an invented quote.
Traditional cuisines of the Mekong · Thailand, Laos, Vietnam, Cambodia, an age-old use
In the rice paddies of the Mekong basin, duckweed, khai-nam ('water eggs'), kai-nam, koonchey depending on the village, is harvested with a net by the women for the soup kaeng om, the green curry, the water-egg omelette. A grain of protein harvested from the surface of a paddy, without tilling, without sowing, without fertiliser, the most efficient agriculture humanity has invented almost by accident.
Bairagi et al. (1999), Duckweed Lemna polyrhiza as a feed ; Skillicorn P., Spira W., Journey W. (1993), Duckweed Aquaculture, Banque Mondiale ; Appenroth K.-J. et al. (2017), Food Chemistry.
Key takeaways
- • Prefers sun to partial shade exposure.
- • Ideal soil: still water rich in nitrogen, 18-30 °c during growth.
- • Classic companion: Water lily (limiting shade).
- • Keep away from: Water primrose.