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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

    Freshwater bodies < 15.5 m deep, drainage ditches.

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

    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.

    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.

    Search tags

RPMP status

Aotea (Exclusion)
Whole region (Sustained Control)
National Pest Plant Accord Species
Lakes Tomarata and Rototoa
Hornwort - Main species image