Hornwort

Status of hornwort in Tasmania

(Ceratophyllum demersum)
Hornwort, photo: Doreen L. Smith
  • Hornwort is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of hornwort are prohibited in Tasmania.
  • The legal responsibilities of landholders and other stakeholders in dealing with hornwort are laid out in the Hornwort Statutory Weed Management Plan.

What does hornwort look like?

  • Hornwort is a free-floating aquatic herb. The branched stems grow from 30 to 60 cm. The leaves are dark green, deeply divided into cylindrical segments which are toothed on one side, and occur in whorls of 5 to 12 leaves. The leaves are very crowded at the ends of stems so as to resemble a bushy animal tail. The flowers are greenish and very small. There are no roots; the roots are replaced by finely divided stem branches.
  • Hornwort overwinters as slowly growing plants, seeds or turions (called winter buds). Flowers are produced in summer but remain fully submerged.
  • Spread is mainly by vegetative means although seed can also be produced. Most spread is via stem fragments or turions which can be broken off by wave motion, foraging animals or boat propellers and floated downstream. Each stem fragment and turion can produce a new colony.
Hornwort, photo: Neal Kramer
Image top: Hornwort, photo: Doreen L. Smith
Image above: Hornwort stem, photo: Neal Kramer

Impacts of hornwort

  • Hornwort is a native plant in ponds, dams and streams on mainland Australia, and only becomes a weed when the freshwater system is altered, particularly where nutrient levels are enriched.

Where does hornwort occur?

  • Hornwort is a native on mainland Australia and occurs in all States.
  • Hornwort has not naturalised in Tasmania.

What you need to do

  • If you locate hornwort anywhere in Tasmania, or if you find a plant that you think could be arrowhead, immediately contact your Regional Weed Management Officer on 1300 368 550 to report this weed.
See also
Hornwort Statutory Weed Management Plan
Weed Links and Resources

Other useful links
Pest Genie
APVMA

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