The common duckweed, whose scientific name is Lemna minor, grows on the surface of water as a free-floating plant. It shares its taxonomic family Lemnaceae with the smallest flowering plant on earth, i.e., wolffia (or watermeal). One of the most interesting facts is that it lacks stem, leaves, and roots (in some species), which are characteristic features of a true flowering plant. Though it causes some potential problems in ponds and other freshwater bodies due to rapid growth, this aquatic plant has several benefits.
If you notice small green plants that cover the surface of garden ponds or stagnant swamps, most likely it's duckweed. There are approximately 38 species of this free-floating, flowering plant. Some of the species lack remnants of the vascular system, while others fail to bear flowers. Mostly adapted in stagnant water bodies like swamps and ponds, it can also grow in slow-moving or quiet streams.
The common duckweed, also known as 'water lentil', is smaller in size than the giant duckweed. The light green, oval, leaf-like structure that floats on the water surface is nothing but thalloid, which may or may not have hairy rootlets on the underside. The thalloid are generally 1 - 3 in number, each measuring less than an inch (1/8-1/16 inch). In polluted or nutrient-rich water bodies, it grows to form dense colonies and covers the water surface completely.
In most cases, duckweed reproduces by means of asexual reproduction, called budding. A single duckweed forms a daughter bud per day. So, you can imagine the growth rate of this aquatic plant. At times, inconspicuous flowers (having one pistil and two stamens) borne on the plants undergo fertilization and sexual reproduction takes place. The fruit is a tiny air-filled structure, and contains a single seed inside.
It is the main source of food for water fowl and several other aquatic inhabitants. In some parts of Asia, this flowering plant is consumed as food. It has the potential to remove as much as 99 percent of dissolved nutrients and wastes from a well-maintained, fish pond system and can be used as a potential remedy for natural water treatment system.
It contains more than 35 percent protein and several other plant pigments and trace minerals. The protein quality of this small aquatic plant is of a superior type, having essential amino acids in high amounts. When introduced in the fish farming system, it is used as a protein supplement for tilapia. Fresh duckweed is fed directly, or it is dried to form fish pellets.
Its another purported use is for the production of biofuel in the future. Its reproduction rate is highest in warm, temperate, and tropical conditions. According to researchers, duckweed doubles its amount within two days, provided that the organic nutrient content is high and growth conditions are favorable. With such a multiplication rate, this common aquatic weed can serve a reliable source of biofuel to meet the ever-increasing energy demands.
When reproducing, it covers the water surface within a short time and blocks sunlight from penetrating in the water body. As a consequence, aquatic plants, insects, and fish are deprived of light. Also, the oxygen supply is reduced significantly, which over time, causes the fish to suffocate and die. Thus, duckweed control becomes a necessity to maintain the pond's ecosystem. Reducing the nutrient flow and manual removal are effective control methods.
In natural water bodies, it provides a habitat for bullfrogs and other pond animals. Considering the ease of its cultivation and rapid multiplication, many scientists have put forth the idea of using this aquatic plant in bioremediation of sewage water and for the production of biofuel.