Common Name: Duckweed

General Information

Lemna minor is a very small, floating plant. It spreads freely and is usually found growing in colonies that can cover quite large areas of still water.
The plant is gathered from the wild for local use as a food and medicine. It can be a troublesome pond weed though it is easily controlled by simply scooping it out[, ]. This scooped out material makes an excellent addition to the compost heap. The growing plant is a good food source for fish and birds, as well as providing cover for creatures in the pond[].

Known Hazards

Although no specific mention has been seen for this species, it belongs to a family where most of the members contain calcium oxalate crystals. This substance is toxic fresh and, if eaten, makes the mouth, tongue and throat feel as if hundreds of small needles are digging in to them. However, calcium oxalate is easily broken down either by thoroughly cooking the plant or by fully drying it and, in either of these states, it is safe to eat the plant.
People with a tendency to rheumatism, arthritis, gout, kidney stones and hyperacidity should take especial caution if including this plant in their diet[].

Botanical References

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Range

A cosmopolitan plant, found in most regions of the world, including Britain, absent from much of the Tropics.

Habitat

Still water[]. Mesotrophic to eutrophic, quiet waters, in sub-oceanic, cool-temperate regions with relatively mild winters[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Perennial
Height	0.01 m
Cultivation Status	Ornamental, Wild

Cultivation Details

Duckweed can be grown from the temperate through to the tropical zones, where it is found at elevations up to 1,500 metres. It grows best in areas where annual daytime temperatures are within the range 7 - 25°c, but can tolerate 5 - 30°c[]. Under freezing conditions, the plant will lay dormant on the pond bottom until warmer conditions return. It can recover from winter temperatures down to -40°c, overwintering as turions (buds), or as seeds, that sink to the bottom of the pond, resting there until warmer conditions return and they can start growing[]. It prefers a mean annual rainfall in the range 700 - 3,000mm, but tolerates 500 - 5,000mm[].
Requires a sunny position in still water that is rich in nitrates and lime[]. Prefers a pH in the range 4.5 - 7.5, tolerating 3.5 - 8.5[].
The plant spreads rapidly across quiet bodies of water that are rich in nutrients, It grows best in water with high levels of nitrogen and phosphate, but will also grow in eutrophic water. Availability of iron is often the limiting factor[].
Wind and wave action can impede duckweed growth and stabilization by disrupting their ability to attach themselves to each other and form their characteristic homogenous colonial populations. Optimal conditions for growth are quiet streams and ponds[].
A full, thick mat of duckweed may have a temperature of about 10°c above ambient air conditions due to radiation[].

Edible Uses

Occasionally used as a vegetable[]. Somewhat harsh in taste compared to Wolffia globosa due to a high content of oxalic acid, though still considered to be far superior to Chlorella algae[].

Medicinal

The whole plant is alterative, antipruritic, antiscorbutic, astringent, depurative, diuretic, febrifuge and soporific[, , ]. It is used in the treatment of colds, measles, oedema and difficulty in urination[].
It is applied externally in the treatment of skin diseases and is used as a wash for ophthalmia[].
The plant is used in homeopathy[], but the report gives no more details.

Agroforestry Uses:

The plant spreads quickly and needs constant removal from ponds in order to prevent it totally covering the surface. The removed material is very high in nutrients and makes an excellent addition to the compost heap[]

Other Uses

The dried plant repels mosquitoes[].

The plant has potential in waste water treatment, absorbing excess nutrients from surface waters, including phosphorus and ammonias, reducing suspended solids, and reducing biochemical oxygen demand[].

Propagation

Seed - we have no information on this species but, since it spreads so rapidly by division, it really needs no extra help once it is in a pond.

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