General description

Submerged aquatic perennial < 7 m tall. Stems are branched and may anchor to sediment or form free-floating mats. Leaves are long, narrow, branched and whorled, with complex architecture. Flowers are minute.

What you need to know

To help protect our environment:

You must not breed, distribute, release or sell hornwort. As hornwort is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.
You must not plant hornwort within the Auckland region.
You must destroy any hornwort on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.
If you see hornwort anywhere on Aotea/Great Barrier Island group, please report it to Auckland Council at pestfree@aucklandcouncil.govt.nz.

Habitats

Freshwater bodies < 15.5 m deep, drainage ditches.

Dispersal

Vegetative spread from stem fragments, dispersed by water. Human-mediated dispersal through contamination of boats, fishing gear and machinery and deliberate cultivation.

Impact on environment

Forms dense stands and displaces native submerged vegetation down to 15m depth. Alters water flow, increases flooding risk and impedes recreational access of water bodies. Likely to negatively impact kōura.

Control

Site Management

Recommended approaches

Do not attempt to undertake control of this species on Aotea/Great Barrier Island group. Also site led control is carried out by Auckland Council at other priority lakes. Please report to Auckland Council if seen.

CAUTION: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Similar species

Parrots Feather

Myriophyllum aquaticum
Parrot's feather has pinnate leaves as opposed to the forked leaves of hornwort.

Eurasian Water Milfoil

Myriophyllum spicatum
E. water milfoil has pinnate leaves as opposed to the forked leaves of hornwort.

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