Pistia stratiotes

Water lettuce

Also known as:

Tropical duckweed

Family: Araceae

Origin: Pantropical

Water Lettuce plants in a plant nursery.
Water lettuce is an aquatic weed that forms floating mats that look like lettuce. Roots are feathery and leaves are light green and hairy to hold air bubbles.
Photo credit: Forest and Kim Starr

Regional Pest Management Plan (RPMP) status

  • National Pest Plant Accord Species
  • Notifiable organism

View more about the RPMP statuses

General description

Perennial floating stoloniferous aquatic. Roots are feathery, clustered and < 45 cm long. Stolons are < 60 cm long and hairy. Leaves are light green, hairy, prominently ribbed, formed in lettuce-like rosettes and have wavy margins.

Flowers are minute and borne in clusters within leaf axils. Fruits are small berries containing wrinkled disc-like seeds.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell water lettuce. As water lettuce is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.

If you see water lettuce anywhere, you must report it to the Ministry of Primary Industries on 0800 80 99 66.


Still and slow-flowing water bodies, lakes, dams, rivers, ponds, streams.


Seeds dispersed by water and wind. Vegetative spread from stolons and budding. Human-mediated dispersal through dumping of aquarium or ornamental pond waste and movement of contaminated boats and equipment.

Impact on environment

Forms dense mats, outcompeting native plants and reducing water quality. Clogs waterways, impeding drainage and recreational activities.


Recommended approaches

Do not attempt to undertake control of this species. The Ministry of Primary Industries will carry out the control of this species.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

A mat of Water Lettuce on the surface of water.
A very invasive weed that must be reported to the Ministry of Primary Industries if seen. Individual water lettuce rosettes can break off and start a new colony.
Photo credit: Forest and Kim Starr
Individual Water Lettuce with water droplets on leaves.
Water lettuce produces tiny flowers that are hard to see and after pollination form small berries with wrinkled disc-shaped seeds. It will form dense mats on the surface of ponds and lakes.
Photo credit: Forest and Kim Starr