What is Duckweed?

Duckweed is a family of flowering aquatic plants that float on the surface of ponds, lakes and other slow-moving bodies of water. Five genera of duckweed have been identified, pictured right. The Wolffia genus contains the smallest known flowering plants on earth. As its name implies, duckweed is eaten by ducks—as well as other animals—and behaves much like a weed: it can grow rapidly on nutrient-rich water, covering ponds in thick green mats.
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Close-up of a pond surface containing Lemna and Wolffia plants. Click to enlarge.
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Representative species from the five genera of duckweed. Click image to enlarge.
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Duckweed naturally covers a pond that receives horticultural runoff at Pinelands Nursery in Columbus, NJ.

Potential Applications of Duckweed

  • A natural wastewater treatment option. The plant feeds on nitrogen and phosphate organic pollutants, the very stuff treatment plants aim to remove from wastewater.
  • The world’s “greenest” animal feedstock. Fast growing, high in protein and dietary minerals, and easily harvested, the plant is cultivated as a feed supplement for chicken, livestock, and farmed fish, especially in developing countries.
  • A renewable and sustainable source of biofuel. Unlike corn, duckweed requires minimal human-made energy to grow and does not deplete the world’s food supply. While duckweed-derived ethanol, like other plant-based fuels, releases carbon dioxide into the atmosphere when burned, the plant absorbs carbon dioxide as it grows, making it carbon neutral.

Finding the Right Duckweed for the Job

There are 37 species of duckweed distributed worldwide, from Siberia to the tropics. Many species grow in multiple locations, forming genetically distinct populations, called strains or clones. The largest collection of duckweed strains—with over 900 accessions (some of which are pictured right)—is housed at the Rutgers Duckweed Stock Cooperative. Researchers in the Lam lab exploit the large genetic diversity of duckweed by systematically comparing strains in the collection; we measure metabolite levels and growth characteristics under a range of environmental conditions. The aim is to find a strain that is well suited for a particular application and environment. For example, strains with a high protein content are ideal for animal feed, whereas strains with a high starch content, the precursor for ethanol, are desirable for biofuels. Ultimately, promising candidates will be tested in the field to determine if large-scale production is technically and economically feasible.
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Duckweed strains belonging to the Rutgers Duckweed Stock Cooperative stored in petri dishes. Click to enlarge.