Duckweed and Watermeal


Duckweed and Watermeal: The World’s Smallest Flowering Plants

Written by: Tyler Koschnick, SePRO Corporation; Rob Richardson, North Carolina State University, Raleigh NC; Ben Willis, SePRO Research and Technology Campus.
This chapter provides an overview of duckweed species and offers tangible tools for identifying common North American duckweeds. The authors provide an introduction to treatment strategies.


  • Aeration relieves the low dissolved oxygen levels caused by large duckweed populations and the chemical treatments that treat duckweed.
  • Duckweeds are typically found in still, nutrient rich waters. Aeration eliminates still, stagnant water.


  • Duckweeds’ small size allows for easy transport by birds, water currents, and boats, contributing to its spread.
  • Duckweeds represent five genera of small floating aquatic plants in the Araxeae subfamily Lemnoideae and include 35 species worldwide.
  • Authors separate duckweed species based on:
    • Frond size, number and shape
    • Root structure or lack thereof
  • Using Grass carp is not a reliable means of managing duckweed due to high stocking requirements and fish size restrictions. Larger fish are no longer effective at straining small plants.
  • Duckweed in the Wolffia (Watermeal) genus are the size of a sugar crystal and are harder to control.
  • Watermeal duckweed are tolerant to Diquat, so foliar applications alone are not recommended to control this plant.
  • Using a combination of systemic and contact herbicides may improve effectiveness and provide longer-term control.

Published: Biology And Control Of Aquatic Plants, A Best Management Practices Handbook. 2014. Editors Lyn A. Gettys, William T. Haller and David G. Petty. Prepared by Aquatic Ecosystem Restoration Foundation: Chapter 15.10

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