What does it look like?
Water lettuce is a free‑floating aquatic plant with thick, pale green, rounded leaves that form a lettuce‑like rosette. The leaves are velvety and hairy, pale yellow‑green, and strongly ribbed, often with a spongy and thickened base. Leaf edges are wavy.
Roots are long, feathery, and finely divided, growing up to 45 centimetres long. The plant spreads by hairy stolons that can reach up to 60 centimetres in length.
Flowers are very small and grow in clusters where the leaves join the stem. The plant produces small berry looking fruits containing wrinkled, disc‑shaped seeds.
Why is it a problem?
Water lettuce is declared an unwanted organism by the Ministry for Primary Industries (MPI) because it’s capable of causing harm to the natural environment, physical resources, or human health in Aotearoa/New Zealand. These species pose a high risk to our environment, economy, recreation, and cultural values.
Water lettuce forms dense mats, outcompeting native plants and reducing water quality. It clogs waterways - impeding drainage and recreational activities.
Seeds are dispersed by water and wind. It spreads vegetatively from stolons and budding. Plus through people, when aquarium or ornamental pond waste is dumped, and contaminated boats and clothing move between waterways.
Control methods
Do not attempt to undertake control of water lettuce. If you see water lettuce anywhere, you must report it to the Ministry of Primary Industries on 0800 80 99 66.
Water lettuce cannot be sold or be in a place where plants are being sold. Plants under the National Pest Plant Accord (NPPA) cannot be propagated, bred, or multiplied, communicated, released, or cause to be released, or otherwise spread.
More information
Water lettuce is not thought to be present in Hawke’s Bay. It’s previously known from sites in Tauranga and Hokianga, Northland, but presumed to be nationally eradicated.
If you see water lettuce anywhere, you must report it to the Ministry of Primary Industries on 0800 80 99 66.
Related links
Management Programme
National Pest Plant Accord
All plants on MPI's National Pest Plant Accord (NPPA) are unwanted organisms under the Biosecurity Act 1993 whose formal or casual trade contributes significantly to their spread.
Plants on the Accord cannot legally be propagated, distributed, or sold in New Zealand. If allowed to spread further, these pest plants could seriously damage our economy and environment.
Notifiable Organism
Any organism specified under the Biosecurity Notifiable Organisms Order 2016 must be reported to MPI if spotted. If any of these organisms become established in New Zealand, they could severely affect our primary production, trade, and market access. If you spot a notifiable organism, you have a legal obligation under section 44 of the Biosecurity Act 1993 to tell MPI. Call the pests-and-diseases hotline on 0800 80 99 66.
More informationSustained Control Programme
Sustained Control exists to hold well-established pests at an acceptable maximum. However, the costs of management and control grow in-step with the size of the invasive population. Because cost:benefit returns can fall to 1:5 or less, most of this work is focused on specific sites of high ecological value. While the spread of these pests between neighbouring properties remains the predominant risk, in some cases control within properties is still sought and warranted. A sustained control programme will hold populations to maximum acceptable limits over the period of the RPMP.
More informationTaxonomies
FamilyAraceae
TypePlants
GroupFloating
HabitatFreshwater
Management ProgrammeNational Pest Plant AccordNotifiable OrganismSustained Control Programme
