Duckweeds, or water lens, are flowering aquatic plants which float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. These plants are very simple, lacking an obvious stem or leaves. The greater part of each plant is a small organized “thallus” or “frond” structure only a few cells thick, often with air pockets (aerenchyma) that allow it to float on or just under the water surface. Depending on the species each plant may have no root or may have one or more simple rootlets.
Reproduction is mostly by asexual budding, which occurs from a meristem enclosed at the base of the frond. Occasionally three tiny “flowers” consisting of two stamens and a pistil are produced, by which sexual reproduction occurs. Some view this “flower” as a pseudanthium, or reduced inflorescence, with three flowers that are distinctly either female or male and which are derived from the spadix in Araceae. Evolution of the duckweed inflorescence remains ambiguous due to the considerable evolutionary reduction of these plants from their earlier relatives.
The flower of the duckweed genus Wolffia is the smallest known, measuring merely 0.3 mm long. The fruit produced through this occasional sexual reproduction is a utricle, and a seed is produced in a sac containing air that facilitates flotation.
Productivity of Duckweeds:
Researchers have done many studies demonstrating the unusually high productivity of this aquatic plant. Dry weight increases of 10-20 tons/ha/yr are the norm. Doubling times in the range of 24 hr have been observed on many occasions, a rate of increase results in 64 g/g dry weight/week, or 73 tons/ha/yr.
Under summer conditions in Louisiana with heavy fertilization, up to 44 tons/ha/yr have been obtained. This rate of production makes duckweed very attractive for cellulosic ethanol or for pelletized fuel.
Needless to say, these rates of increase will be negatively affected by diminished rates of fertilization or cold weather in the temperate zone. However, it is clear that the species of this group are capable of a level of productivity closer to that obtained with microorganisms than with other higher plants.
The high levels of fertility required to obtain this massive growth of duckweeds might seem to be an obstacle, but in fact are economically feasible. One example of nutrients for duckweed would be nitrogenous runoff wastes from feedlots.
For additional links about Duckweed check out this boatcycle.com link.