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.
Colony on a small pool
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 thinned by seining
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.