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
To prevent the establishment of the subject, or an organism being spread by the subject, that is present in New Zealand but not yet established in an area.
National Pest Plant Accord (NPPA)
The NPPA is designed to prevent the sale, distribution and propagation of a set list of pest plants (the Accord list) within New Zealand. If allowed to spread further, these pest plants could seriously damage the New Zealand economy and environment.
More informationUnwanted 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.
Rules
Sections 52 and 53
Sections 52 and 53 of the Biosecurity Act 1993, which prevent the communication, release, spread, sale and propagation of pests, must be complied with.
Taxonomies
FamilyMenyanthaceae
TypePlants
GroupFloating
HabitatFreshwater
Management ProgrammeExclusion ProgrammeNational Pest Plant Accord (NPPA)Unwanted Organism
RulesSections 52 and 53
