Menyanthaceae - Nymphoides geminata

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 and 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 and tolerates fluctuating water levels.

Not known to set seed in New Zealand.  Vegetative spread from stem, leaf fragments and deliberate human-mediated dispersal as a pond ornamental.

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