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.
Still or slow-moving water bodies including lake margins, streams, wetlands, drains, farm dams. Grows at wide range of water depths, from exposed mud to water c.2.5 m deep.
Why is it a problem?
Marshwort rapidly colonises shallow water, forming dense mats which block waterways and smother other aquatic plants. It has a history of invasiveness overseas and closely related taxa are also invasive. It can rapidly out-compete other ornamental lily species. Tolerates fluctuating water levels.
Not known to set seed in New Zealand. Vegetative spread from stem and leaf fragments. Deliberate human-mediated dispersal as a pond ornamental.