Rootless Duckweed

Species: Wolffia arrhiza

weed identification

common name
Spotless Watermeal, Rootless Duckweed

Wolffia arrhiza is a free floating freshwater aquatic plant and is the smallest vascular plant on earth. The green part of the plant, the frond, is a sphere measuring about 1 mm wide, but with a flat top that floats at the water’s surface. It has no roots.


Stationary and slow-moving water bodies, especially where nutrients are high. E.g. ornamental ponds, fish ponds, dams, irrigation dams. Rarely found in Australia

native or exotic?

It reproduces mainly vegetatively by division, with the rounded part budding off into a new individual. When the weather becomes cooler, a turion* is produced and sinks to the bottom of the water body, where it lies dormant throughout winter. During warmer weather, it rises to the surface of the water to begin the growth process again. *Turion (a type of bud that is capable of growing into a complete plant).


Attaching to animals such as waterfowl, human activity or floods.


Important food source for aquatic fauna.

What does Rootless Duckweed look like?

Use these images below to help you decide whether you are dealing with Rootless Duckweed.

Disadvantages of Rootless Duckweed

Full coverage of a pond or dam by Duckweed can cause significant problems such as:

  • Stopping oxygen diffusion
  • Shades out all submerged vegetation preventing further growth and causing death
  • Causes fish and other aquatic life death
  • Provides breeding ground for mosquitos
  • Changes the water chemistry to favour harmful algae and bacteria
  • If left untreated, Duckweed can render the water unusable and make treatment far more costly than if initially dealt with


Orange Oil – Designed to treat free floating organic matter. This treatment is best applied when 20% of the surface water is still visible, and is intended to be used over multiple treatments (day 1, 2 and 4).

AQ200 Aquatic Herbicide + Wetting Agent – Chemical Herbicide designed to kill free floating weeds quickly. Use on mild to severe infestations.

Aquatic Weed Skimmers – Physically remove free floating weeds. Use on mild infestations or to aid herbicide treatments.

Aquatic Harvesting – Large amphibious machine that clears the surface of floating aquatic weeds. Book this service for severe infestations or for larger water bodies.

prevention options

Surface Clear – Creates a protection barrier on the surface of the water to limit plant replication and new infestations forming. Use on its own or after herbicide treatments.

Aerating Fountains – Reduces the severity and likelihood of aquatic weed infestations. Use in any body of water.