Quick Facts

Quick facts

• Hornwort (Ceratophyllum demersum) is a free-floating, submerged, rootless, leafy, annual or perennial freshwater herb, reproducing vegetatively and by seed.
• It occurs in sheltered sites in stagnant or slowly moving water in ponds, dams, streams and reservoirs.
• Hornwort is native to Australia, occurring in all states except Tasmania.
• In Australia, Hornwort rarely causes problems when it is in balance with the surrounding ecosystem and can be beneficial. However, when environmental change occurs, the plant becomes weedy and has a negative effect on stream flow, interferes with navigation, fishing and hydro-electric output.
• Herbicides provide the best means of controlling the growth of Hornwort.

What Does It Look Like?

What is it?

Hornwort (Ceratophyllum demersum) is a free-floating, submerged, rootless, leafy, annual or perennial freshwater herb, reproducing vegetatively and by seed. The stems are freely branching, to 60 cm in length. The leaves are dark green, in 5–12 whorls, 1–4 cm long and two or three times palmately divided.

The flowers are greenish, very small to 1 mm long, unisexual, solitary and stalk-less, at the junction of the stems and leaf bases.

The one-seeded fruits are black, ellipsoid, 4-5 mm long with 2 basal spines, 9-12 mm long, and topped by the persistent spine-like style (Parsons & Cuthbertson 2001).

For further information and assistance with identification of Hornwort contact the herbarium in your state or territory.

Flower colour

White, Green

Growth form (weed type/habit)

Herb, Aquatic

Where it currently grows? Preferred habitat

Hornwort occurs in sheltered sites in stagnant or slowly moving water in ponds, dams, streams and reservoirs (Parsons & Cuthbertson 2001). It grows best in slightly alkaline water and when the water is rich in nitrogen (Sainty & Jacobs 2003).

Are there similar species?

Hornwort can be commonly mistaken for species of Milfoil (Myriophyllum spp.) and Fanwort (Cabomba caroliniana). This is because their submerged foliage looks very similar. The Milfoils and Fanwort have both emergent and submerged leaves, often of different shape, whereas Hornwort has only submerged leaves. The leaves and stems of Fanwort are covered with a thin gelatinous coating, unlike those of Hornwort. Also, the flowers of Fanwort and the Milfoils are emergent whereas the flowers of Hornwort remain fully submerged (Sainty & Jacobs 2003).

Why Is It A Weed?

What are its impacts?

Native ecosystems: In Australia, Hornwort rarely causes problems when it is in balance with the surrounding ecosystem. It oxygenates water and provides food for aquatic herbivores. However, when environmental change occurs, especially nutrient enrichment, the plant becomes weedy and has a negative effect on stream flow, interferes with navigation, fishing and hydro-electric output (Parsons & Cuthbertson 2001; Tasmanian Department of Primary Industry and Water 2007).

How does it spread?

Although Hornwort reproduces both sexually and asexually, the environmental requirements for sexual reproduction limit seed production in many areas. The hooked spines on the fruit catch in the feathers of water birds and on waders clothing and can be spread in this way. The two modes of vegetative reproduction, fragmentation and turion (winter buds) formation, are probably the principal means of dispersal. The fragile plant readily fragments when disturbed by strong wave motion, foraging animals or propeller-driven boats. Each fragment is capable of forming a new colony. Turions may also travel considerable distances in water flow, either attached to stem fragments or as individuals, while gradually sinking to the mud at the bottom (Parsons & Cuthbertson 2001).

What is its history in Australia?

Hornwort is native to Australia, occurring naturally in all states and territories except Tasmania and the Australian Capital Territory (Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

Chemical control: Herbicides provide the best means of controlling the growth of Hornwort. Short-exposure chemicals are usually necessary to minimise damage to non-target species.

Non-chemical control: Mechanical control: Mechanical harvesting gives only temporary relief and encourages further growth by fragmentation. In overseas experiments, season-long control has been obtained by covering affected areas with black plastic sheeting for 18-28 days. This is practical only in smaller contained areas such as ponds and dams (Parsons & Cuthbertson 2001).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Hornwort seeds and turions (winter buds), germinate in spring in the mud of streams and ponds. Turions are the specialised tips at the end of the stems, which remain attached to the parent plant or break free, producing new plants. The primary stem elongates to about 8 cm and then breaks free from the bottom mud and rises to the surface, growing and branching as the season progresses. Flowers are produced in summer but remain fully submerged. Stamens are shed as the male flowers mature and, forming floats, rise to the surface as a group, release the pollen, which sinks and makes contact with the female flowers. The hard-skinned fruits sink to the bottom at maturity. In cooler regions, more plants germinate via turions than seed (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD, SA, VIC, WA

What areas within states and territories is it found?

Hornwort grows all along the east coast of Australia, occasionally reaching pest proportions in parts of south-eastern Queensland. In inland New South Wales, it is recorded at several places along the Murray River and in the Lachlan River. South Australian colonies occur at Mannum and near Lake Alexandrina. In Victoria, Hornwort is found near Kyabram in the Goulburn Valley and in Gippsland, occasionally becoming weedy in the Maffra-Sale drainage channels. Hornwort is also recorded throughout the Top End of the Northern Territory and the Kimberley in Western Australia (Parsons & Cuthbertson 2001; Western Australian Herbarium 1998 -). There are no known naturalised hornwort populations in Tasmania. However, the plant has been recorded in aquaria in that state (Tasmanian Department of Primary Industry and Water 2007).

Where does it originate?

Hornwort is a truly cosmopolitan plant. Despite being quite fragile, in that it is killed by ice, sea water and desiccation, it occurs on all continents of the world, including Australia, in temperate and tropical zones and on many oceanic islands (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

TAS

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Ceratophyllum demersum

Other scientific names (synonyms)?

Does it have other known common name(s)?

Arigma, Common Coontail, Gang Gang, Hornblad, Hornweed, Matsumo