Common duckweed (Lemna gibba)

Also known as: fat duckweed
Synonyms: Lemna cordata, Lemna parodiana, Lenticula gibba, Lenticula gibbosa, Limna cordata, Limna parodiana, Telmatophace gibba, Telmatophace gibbosa
French: Lenticule Bossue, Lentille Bossue
GenusLemna (1)
SizeRoot length: 15 mm (2)
Diameter: 1.5-5 mm (2)

Common duckweed is classified as Least Concern (LC) on the IUCN Red List (1).

This duckweed is one of Britain's most common small water plants, which forms familiar green mats covering stagnant water bodies (4). It has a simple plant body, known as a thallus, which floats on the surface of the water and measures up to five millimetres in diameter (2). A single root hangs down into the water (2).

Widespread throughout Britain, but is absent from much of Scotland and Shetland (2). Elsewhere the species has a very wide global distribution, absent only from polar areas and the tropics (2).

Found in a wide range of still or slow-flowing water bodies, common duckweed can also occur on mud or damp rocks (3).

This species spreads mainly through vegetative reproduction (3), but flowers are occasionally produced in shallow water exposed to the full sun (2). When covering the entire surface of a pond, it can make the water appear solid, and in parts of the north-west of England children were scared away from such ponds by the myth of Jenny Green-teeth, a pond elf or monster whose presence was indicated by duckweed; she was said to lure children into ponds and drown them (5).

Not currently threatened.

Not relevant.

For more information on British plants and their conservation see


This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (June, 2011)
  2. Clapham, A.R., Tutin, T.G. and Moore, D.M. (1987) Flora of the British Isles. 3rd Edition. Cambridge University Press, Cambridge.
  3. Preston, C.D., Pearman, D.A. and Dines, T.D. (2002) The New Atlas of the British and Irish Flora. Oxford University Press, Oxford.
  4. Mabey, R. (1996) Flora Britannica. Sinclair-Stevenson, London.
  5. Grigson, G. (1996) The Englishman’s Flora. Helicon, Oxford.