Hornwort
Botanical Name
Ceratophyllum demersum
Family
Ceratophyllaceae (hornwort)
Also known as
Hornweed, coontail, lakeweed
Where is it originally from?
Asia, Africa, Australia, Malaysia, and North America
What does it look like?
Submerged, free-floating or anchored perennial that grows in water up to 16m deep. No roots are present, and it is usually lightly anchored by buried stems and leaves. Stems (30-150 cm long) are floating or submerged, branched, stiff and brittle. Thin dark green leaves (1-4 cm long) in whorls of 7-12 are densely crowded at the stem tip, increasingly spaced down the stem, and equally forked once or twice into stiff tapering segments with teeth on the outer edge. Produces minute green or white flowers, but is not known to fruit in New Zealand.
Are there any similar species?
Myriophyllum species have feathery not forked leaves, and their leaves are not stiff.
Why is it weedy?
New plants can form from each piece of the easily broken stems. Rapidly invades water of varying clarity, temperature, light and nutrient level, and dense growth habit crowds out native species. There are no native plants of a similar height to compete with it.
How does it spread?
Fragments are spread within catchments by the flow of the water. New catchments are infested when fragments are transported by contaminated boats and trailers (and occasionally motor cooling water), eel nets, diggers, and people liberating fish.
What damage does it do?
Forms dense beds, shades out smaller native species and prevents them establishing. It can contribute to blockages of waterways and flooding. Rotting vegetation stagnates water, killing fauna and flora. Threatens most submerged plant communities.
Which habitats is it likely to invade?
Still or slow-moving waterbodies and lagoons. It could potentially establish throughout New Zealand.
What can I do to get rid of it?
Hornwort is thought to be eradicated in the South Island. If you are in the South Island and suspect you have found hornwort, report all sightings to the MPI hotline (Ph 0800 80 99 66) as soon as possible.
If you are in the North Island contact your nearest regional council or Department of Conservation office for advice on rules and control options.
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