Lemna minor (common duckweed or lesser duckweed) is a species of Lemna (duckweed) with a subcosmopolitan distribution, native throughout most of Africa, Asia, Europe and North America, occurring everywhere that freshwater ponds and slow-moving streams occur, except for arctic and subarctic climates. It is not reported as native in Australasia or South America, though is naturalised there.
It is a floating freshwater aquatic plant, with one, two or three leaves each with a single root hanging in the water; as more leaves grow, the plants divide and become separate individuals. The root is 1-2 cm long. The leaves are oval, 1-8 mm long and 0.6-5 mm broad, light green, with three (rarely five) veins, and small air spaces to assist flotation. It propagates mainly by division, and flowers are rarely produced; when produced, they are about 1 mm diameter, with a cup-shaped membranous scale containing a single ovule and two stamens. The seed is 1 mm long, ribbed with 8-15 ribs.
It grows in water with high nutrient levels and a pH of between 5 and 9, optimally between 6.5 and 7.5, and temperatures between 6 and 33 °C. Growth of colonies is rapid, and the plant frequently forms a complete carpet across still pools when conditions are suitable. In temperate regions, when temperatures drop below 6 to 7 °C it develops small, dense, starch-filled organs called 'turions', which become dormant and sink to the water bottom for winter; the following spring, these recommence growth and float back to the surface.
It is an important food resource for many fish and birds (notably ducks); it is rich in protein and fats. Birds are also important in dispersing the species to new sites; the root is sticky, enabling the plant to adhere to the plumage or feet while the bird flies from one pond to another.
Cultivation and uses
It is often used as a plant in both coldwater and tropical aquaria as well as in outdoor ponds, though it must be frequently cut back because of its rapid growth rate and may be considered a pest. It is also grown as a commercial crop for animal feed, primarily for fish and poultry, as it is fast-growing and easy to harvest by surface skimming.
Population and Competition
Lemna minor is structurally adapted to grow quickly. That enables it to populate bodies of water rapidly. It overcomes inter-species competition by growing a thick carpet over still water bodies, thereby shading out other plant species below it and eliminating the competition. With intra-specific competition, it will compete by absorbing as much of its surrounding resources as possible so that it has the energy to grow and reproduce.
- Germplasm Resources Information Network: Lemna minor
- Den Virtuella Floran: Northern Hemisphere map
- Flora of NW Europe: Lemna minor
- Flora of North America: Lemna minor
- Plants of British Columbia: Lemna minor
- FAO: Duckweed - a potential high-protein feed resource for domestic animals and fish
- Lemna minor
- Missouri Botanical Garden: Duckweed Roots
- Hiscock, P. (2003). Encyclopedia of Aquarium Plants. United States and Canada: Interpret Publishing. ISBN 0-7641-5521-0.