Lemna minor - Common Duckweed

Lemna minor, also known as the Lesser Duckweed, is one of the most common species of cosmopolitan duckweed, as it is found in slow and stagnant waters in most countries in Africa, Asia, Europe, and North America. It is a small floating aquatic plant with oval leaves measuring a few millimeters. Deciduous, it spends the winter underwater and resurfaces in spring. This species thrives in bright light and easily colonizes freshwater with high nitrate levels and rich in organic matter. Excessive proliferation can hinder the proper development of rooted aquatic plants, depriving them of light. It is reserved for use in aquariums where certain species may appreciate the filtered and diffuse light under a blanket of duckweed.

Lemna minor belongs to the arum family. While this floating aquatic perennial is very common in calm waters worldwide, it is absent from Arctic and subarctic climates and high mountains. It reproduces rapidly when exposed to suitable sunlight and temperature. In certain contexts, this duckweed has strong potential for water purification and as organic fertilizer or food, but it can also quickly bioaccumulate certain non-biodegradable pollutants and transfer them to other compartments of the environment. It is a small floating plant, kept afloat by an internal air reserve. Its oval leaves measure 1 to 8 mm long and 0.6 to 5 mm wide. They are light green on the upper surface and darker on the lower surface. The lower surface is flat or slightly undulate. Each mature leaf bears a single central root (usually 1 to 2 cm long); this root, white to greenish, almost always descends vertically into the water. On each individual, small buds sprout from the leaves and eventually separate to form a new plant. In cool and temperate zones, when the water temperature drops below 6 to 7 °C, the duckweed produces starch granules that are stored in a structure called a "turion". The plant dies, and the turion sinks into the water where it will spend the winter. In spring or early summer, a seedling forms and grows, floating on the surface, and the seasonal cycle begins again.

Lemna minor can be used in aquaria to purify water and create less illuminated submerged areas, appreciated by certain species of plants or fish. It is important not to use it in open natural environments, where it is considered harmful and has an impact on biodiversity. Its rapid proliferation leads to the formation of dense mats on the water surface, preventing the penetration of light and gas exchange between air and water. This can result in the asphyxiation of the environment, which is highly detrimental to other species (fauna and flora), as well as the rapid accumulation of organic matter that cannot be degraded without oxygen. Duckweeds also absorb mineral salts in large quantities and therefore tend to impoverish the aquatic environment.