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NZ Ex Games
The Hit List

Verified public Target identity

freshwater · flora / algae

Hornwort

Ceratophyllum demersum

Also known as Coon’s tail

Hornwort showing stiff forked leaves arranged in dense whorls.
Hornwort showing stiff forked leaves arranged in dense whorls. Sdjurovic · CC BY-SA 4.0

Visual markers

  • Dark-green submerged stems with stiff leaves arranged in whorls around the stem.
  • Each narrow leaf forks one or more times and has small, conspicuous teeth along an edge.
  • The plant has no true roots; lower leaves or buried stem bases may anchor it in sediment.
  • Check the leaf arrangement and forked, toothed segments at close range; detached fragments may float or wash ashore.

What

Hornwort is an introduced, submerged perennial aquatic plant. It has no true roots and spreads in New Zealand mainly when its brittle stems break into fragments.

Why

Hornwort can form tall, dense, single-species beds that displace indigenous aquatic plants and interfere with recreation, water flow, irrigation and hydro-generation.

Where

It is widely naturalised through much of the North Island, especially in the Waikato River and Rotorua lakes. Current local presence requires up-to-date authoritative or verified evidence.

Identification notes

  • Egeria: Egeria has broader, undivided leaves in whorls and produces true roots. Compare dossier.
  • Lagarosiphon: Lagarosiphon has simple alternate leaves with downward-curving tips. Compare dossier.

Keep in mind: Submerged form varies with growing conditions. Overseas morphology images can support identification, but do not establish New Zealand occurrence or impact.

Supporting images

  • Hornwort morphology showing whorled, repeatedly forked leaves; photographed overseas and not evidence of New Zealand occurrence.
    Hornwort morphology showing whorled, repeatedly forked leaves; photographed overseas and not evidence of New Zealand occurrence. Anastasiia Merkulova · CC BY 4.0

Established knowledge

For consequential field decisions, consider the knowledge state and cited sources for each claim, and consult authoritative guidance where appropriate. Information and reliance terms

50% reference coverage — not scientific certainty or ecological progress
  • Identification
  • NZ status
  • Ecological impact
  • Sources

Open knowledge

These are parts of the public picture that could become clearer with better evidence.

  • Distribution
  • Visual clues
  • Confusion species
  • Regional intelligence
Sources & credits
Prepare related field media

Field observations

Field observations connect sightings and signs with a place, time and source. They can support evidence after review. This dossier does not accept public submissions.

No field observations are published for this Target.

Commentary

Local experience, corrections and context help explain the public record. Commentary is not verified knowledge. This dossier does not accept public comments.

No commentary is published for this Target.

Questions and Missions

What can the sources tell us, and what still needs evidence? Explore dossier discoveries and research questions to understand this Target. Research leads identify knowledge gaps; they are not field assignments.

Explore Missions and Hunt mode for Hornwort
  • Where is hornwort currently established or emerging in New Zealand?Research question · evidence needed
  • What evidence distinguishes current ecological impact from presence alone for hornwort?Research question · evidence needed
  • Which reusable images verify hornwort growing in situ or forming infestations in New Zealand?Research question · evidence needed

Shout Out

Shout Out

Share this record so others can explore the same question, place or ecological work. The link keeps its context and sources together.

Hornwort showing stiff forked leaves arranged in dense whorls.

Hornwort — The Hit List — NZ Ex Games

Canonical link

/hit-list/weed-hornwort
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