Duckweed are tiny but robust plants, which can quickly cover a whole pond in an unbroken mat of green. This makes them excellent subjects for students to use to develop investigations.

Practicals

• Duckweed are useful plants for students to use to develop investigations. Student Project: Investigations with Lemna Minor.
• These plants are very useful for investigations on population growth. They are so tiny you can grow them plastic cups, where they grow and reproduce vegetatively on the water’s surface In this practical on measuring duckweed, you can either collect duckweed from the a pond, or from a lab aquarium.
• Beyond the classroom, duckweeds are used for the bioremediation of fresh water – they can lower the concentration of toxic ions in the water, incorporating them into their tiny forms.
• Duckweed and Green Algae can be used for investigations into the effects of eutrophication

Articles

• Robinson, G. (1988), Experimental method and biological concepts demonstrated using duckweed. School Science Review, 69 (248) 505-508

Teaching Topics

• Student investigations
• Population growth

Description

Duckweed. Lemna minor

Duckweeds are robust, tiny flowering plants. They often form an unbroken mat on the flat surface of still water, in aquaria, ponds, ditches and lakes. In fact they are most wide-spread free floating macrophyte in Britain

Growing and sourcing

Obtaining: Both Sciento and Blades Biological supply duckweed for schools.

Care: Lemna minor grows best at a fairly low nutrient level. It does not compete well with algal blooms. To create the low nutrient levels in water, we suggest boiling one wheat grain in a little distilled water and then making it up to a litre volume. Put the duckweed on top. They should double every three days at 22ºC. Sycamore and maple leaves have also been reported as a good nutrient source. The pH should be between 6 and 8.