Common name: Hornwort

Botanical name: Ceratophyllum demersum

Management programme: Exclusion


Why is it a pest?

It sounds like the name of something from the magical world of Harry Potter but unfortunately hornwort threatens most underwater plant communities, negatively affecting the environment and recreational values. It rapidly invades water with all different levels of clarity, temperature, light and nutrient level. Its thick growth crowds out native species, can block waterways, and the rotting vegetation stops the flow of water which kills fauna and flora.



Exclusion programme

The exclusion programme aims to stop certain pests that are in very low numbers or in surrounding areas from establishing in Otago.




What does it look like?

Hornwort is an underwater, free-floating or lightly-anchored plant that grows in water up to 16m deep. Its stems are floating or submerged, stiff and easily broken. It has thin, dark green leaves in patterns of spirals of 7-12 and are densely crowded at the stem tip. They get more and more spaced out down the stem. It produces tiny green or white flowers but is not known to flower in New Zealand. New plants can form from each piece of the easily-broken stems.

Click here to see images


What are the rules?

While there are no rules for landowners in Otago regarding hornwort, if it gets into Otago, ORC would take the lead role in control. Over the life of the pest plan (10 years), the goal is to stop hornwort establishing in Otago, to prevent negative effects on economic well-being and environmental values.


How will we achieve that?

ORC will be responsible for controlling the plant if it gets into Otago, most likely in collaboration with the Ministry for Primary Industries, Department of Conservation, Land Information New Zealand, and land occupiers. Please let us know if you think you have spotted hornwort by calling us on 0800 474 082 or emailing biosecurity@orc.govt.nz


How can I control it?

If you think you have hornwort, please let us know by calling us on 0800 474 082 or emailing biosecurity@orc.govt.nz and we will take care of controlling it.

To make sure you are not spreading any aquatic pests, the Check, Clean, Dry method is the best way to keep our waterways pest-free. Click here for more information on Check, Clean, Dry.



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