What does it look like?
Marshwort is a bottom-rooted perennial water lily-like plant. It has long-branched running stems, several metres long. The stems lie just beneath the water surface, producing groups of leaves, roots, and flowers. The leaves are 30-80 mm long, broadly ovate and are smaller than the leaves of other water lilies.
Marshwort has bright-yellow flowers with five petals and hair-like margins, which sit above the water surface on long stalks that grow in pairs. The flowers are 25-35 mm wide and have fringed wings. Flowers are produced from November through to April.
It prefers still or slow-moving water bodies including lake margins, streams, wetlands, drains, and farm dams. Marshwort grows at a wide range of water depths, from exposed mud to water 2.5 m deep.
Why is it a problem?
Marshwort rapidly colonises shallow water, forming dense mats which block waterways and smothers other aquatic plants. It has a documented history of invasiveness in other countries, and closely related species have also demonstrated invasive behaviour.
It can rapidly out-compete other ornamental lily species and tolerates fluctuating water levels.
Marshwort is not known to set seed in New Zealand. It spreads vegetatively through stem and leaf fragments, as well as through intentional human-mediated dispersal for use as a pond ornamental
Control methods
Marshwort is an Exclusion Pest under the Hawke’s Bay Regional Council Regional Pest Management Plan 2018-2038 and not known to exist in Hawke’s Bay.
If you think you have seen Marshwort, do not attempt to control it yourself.
Please contact us on 06 835 9200.
Related links
http://apps.mpi.govt.nz/applications/nzpests-view/Article/634/Marshwort
http://www.nzpcn.org.nz/flora_details.aspx?ID=3247
http://www.nzflora.info/factsheet/Taxon/Nymphoides-geminata.html
https://www1.maf.govt.nz/uor-cgi/uor.pl/show?species_id=36696
https://www.weedbusters.org.nz/what-are-weeds/weed-list/marshwort/
Notify Council
If you think you've found this pest, please get in touch with our Biosecurity Team at biosecurity@hbrc.govt.nz or call us on 0800 108 838.
Management Programme
Exclusion Programme
Exclusion pest plants are organisms known in other parts of the country but are not thought to exist in Hawkes Bay. An Exclusion Programme aims to prevent a specific pest from establishing in the region before it arrives. With economic returns of around 1:100, prevention is always the most cost-effective strategy available. The faster we can detect an incursion, the more economical and successful our response efforts are likely to be. If an organisms listed under an exclusion programme was to establish, it has the potential to cause adverse effects on production, economic wellbeing, and environmental values.
More informationNational 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.
Unwanted Organism
An unwanted organism is any organism that's capable of causing harm to natural or physical resources (like forests and waterways) or human health. A number of introduced pests in New Zealand are classed as unwanted.
More informationRules
Sections 52 and 53 of the Biosecurity Act (1993)
No person shall knowingly communicate, cause to be communicated, release, or cause to be released, or otherwise spread any pest or unwanted organism, in accordance with Sections 52 and 53 of the Biosecurity Act 1993
More informationSection 26ZM of the Conservation Act (1987)
In accordance with the Conservation Act 1987 section 26ZM, no person shall transfer live aquatic life or release live aquatic life into any freshwater. This includes native or introduced fish, plants, and invertebrates. The taking and holding of some organisms requires a special permit from MPI.
More informationTaxonomies
FamilyMenyanthaceae
TypePlants
GroupFloating
HabitatFreshwater
Management ProgrammeExclusion ProgrammeNational Pest Plant AccordUnwanted Organism
RulesSections 52 and 53 of the Biosecurity Act (1993)Section 26ZM of the Conservation Act (1987)
