duckweed

Duckweed refers to several species of small, free-floating aquatic plants in the family Araceae (subfamily Lemnoideae). The most common genera are Lemna, Spirodela, Landoltia, Wolffia, and Wolffiella. Duckweeds are among the smallest flowering plants, typically forming dense, floating mats on still or slow-moving freshwater bodies. Individual fronds range from about 1 to 8 mm for most Lemna species, though some Wolffia species are under 1 mm and rootless.

Morphology and reproduction: Duckweeds are usually simple, herbaceous, green to yellow-green fronds that float on the surface. Most species have a short-lived root that hangs into the water column, providing some nutrient uptake, but several species (notably Wolffia and Wolffiella) are rootless. Reproduction is predominantly asexual, through rapid budding and fragmentation of fronds, leading to exponential growth. Sexual reproduction occurs in some species under favorable conditions and yields tiny seeds or sporocarps.

Ecology and uses: Duckweeds rapidly form surface mats, shading and competing with submerged vegetation and altering gas exchange. They uptake nutrients such as nitrogen and phosphorus, contributing to nutrient cycling and water purification in constructed wetlands and wastewater treatment. They are an important food source for waterfowl and aquatic invertebrates. They have potential as animal feed protein, a source for biogas or biofuel research, and for phytoremediation. Some species can be weedy or invasive in disturbed habitats.

Management: In natural settings duckweed abundance is influenced by light, temperature, nutrient availability, and grazing pressure. In ponds and canals they can clog intakes and reduce oxygen exchange; control methods include shading, nutrient management, mechanical removal, and biological control in some cases.