Quick Facts

Quick facts

  • Praxelis (Praxelis clematidea), a native plant of subtropical South America, is an annual or perennial herb 0.2–1 m tall.
  • Disturbed areas such as roadsides, fencelines, railway lines, run-down pastures and plantations are all at risk from infestation.
  • Contact your state or territory weed management agency or local council if you find Praxelis, especially any infestations outside its known distribution. Any new information on its presence is extremely important.
  • Seed dispersal is aided by machinery and vehicles.
  • Prevention is the most cost-effective form of weed control, keep uninfested areas free of Praxelis, and do not attempt control on your own.

What Does It Look Like?

What is it?

Praxelis is an annual or perennial herb 0.2–1 m tall. Its leaves are arranged in opposite pairs along the brittle cylindrical stems, which are covered in short soft hairs. The leaves are tear-shaped or 'ovate' to diamond shaped or 'rhomboid', with a conspicuously toothed margin containing between five and eight teeth. When crushed the leaves emit a pungent odour similar to cat's urine.

The flowers are in conical to bell-shaped heads (a key identifying feature of the species) each with 30–50 lilac or bluish florets and occur in groups at the ends of stems.

The seeds (called achenes) are black, 2–3 mm long, black, with a tuft of 15–40 white pappus-bristles at the apex (Veldkamp 1999; CRC 2003).

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

Flower colour


Growth form (weed type/habit)


Where it currently grows? Preferred habitat

Praxelis invades a range of habitats in the tropics and subtropics. It is particularly suited to disturbed areas such as roadsides, railway lines and fencelines, and rapidly colonises bare earth following fire. Able to survive on a range of soil types, it invades crops, grasslands and, particularly, over-grazed pastures. It can become the dominant herbaceous plant in open eucalypt woodlands, and grows vigorously along riverbanks. It tolerates partial shade to full sun but does not cope well under heavy shade. Praxelis is well established in areas that have more than 900 mm annual rainfall and is expected to survive in areas with annual rainfall in the range 500–700 mm. In these drier areas Praxelis behaves more like an annual, setting seed and dying off until the next rainy season, when germination takes place. It will probably only exist in cultivated areas or along waterways in areas where annual rainfall is less than 500 mm (CRC 2003).

Are there similar species?

Praxelis is very similar to two related weed species, Ageratum conyzoides and Ageratum houstonianum, which are also found in northern Australia. These species are commonly known as 'Blue Top' and 'Billy Goat Weed', and are often mistaken for each other. Both are found as environmental weeds, especially on roadsides and disturbed areas.

The differences between Praxelis and A. conyzoides are subtle, even to the trained eye. Both have blue flowers, although those on A. conyzoides are often less intense blue and may also be white or pale lilac. Both are covered with hairs, although the hairs on Praxelis are longer and more conspicuous. The main difference is that Praxelis has a conical receptacle for its 'florets', the dense cluster of small flowers that make up the flower head, whereas A. conyzoides has a flat or slightly dome-shaped receptacle. Also, the ring of 'bracts', modified leaves that surround and support the flower head, is deciduous and drops off Praxelis flowers, whereas in A. conyzoides the bracts are persistent. The leaves of Praxelis have a more pungent odour when crushed, and are more triangular and more sharply toothed than those of A. conyzoides, which are more rounded near the tip and have smooth teeth along the edges. Finally, the 'pappus' on Praxelis seeds consists of many more bristles (15-40) than A. conyzoides, which has only about 5 bristles. The flower colour and size of A. houstonianum is usually much closer to that of Praxelis than A. conyzoides, especially in those parts of northern Queensland where the three species occur together (e.g. Atherton Tablelands) (CRC 2003).

Why Is It A Weed?

What are its impacts?

Praxelis is on the Alert List for Environmental Weeds, a list of 28 non-native plants that threaten biodiversity and cause other environmental damage.

Agriculture: Praxelis could threaten, and significantly increase the costs of managing, such crops as bananas, other fruits and sugar cane.

Native ecosystems: An invader of both disturbed and relatively undisturbed areas, Praxelis has the potential to seriously degrade Australia's ecosystems. It could infest pastoral grasslands and conservation areas, particularly open eucalypt woodlands. There is some evidence that it may be poisonous to stock and humans if ingested (CRC 2003).

How does it spread?

Praxelis mainly spreads by seeds. It can produce large numbers of seeds in as little as three or four months after germinating. The seeds possess a 'pappus', a tuft of barbed bristles that can help them spread by wind or water, or by attaching themselves to animal fur and feathers, clothing or machinery. Long distance dispersal is mainly attributed to seed attached to vehicles or carried as accidental contaminants of building supplies and landscaping materials. Praxelis is also capable of vegetative growth, in which roots and new plantlets form along branches in contact with the soil (CRC 2003).

What is its history in Australia?

Praxelis was first recorded in Tully and Innisfail, Queensland, in 1993 but was probably present there for about 20 years before being positively identified. It is spreading extremely quickly and effectively throughout northern and eastern Queensland – an isolated infestation recently found in Gympie is some 1200 km by road south of the nearest infestation in Townsville. Praxelis is thought to have first entered Australia in a batch of contaminated seed from Brazil between 1965 and 1975. It is believed to have been part of the same seed batch that also included Siam weed, Chromolaena odorata – a closely related species also on the Alert List for Environmental Weeds – because the two species were first found growing in very close association in the Tully region. Although it was recognised by landholders in the area as a weed, it was not formally identified as Praxelis until 1993 during the initial investigations into the Siam weed infestation (CRC 2003).

How To Manage It?

Best practice management

Early detection and eradication are important to prevent infestations of Praxelis. Small infestations can be easily eradicated if they are detected early but an ongoing commitment is needed to ensure new infestations do not establish. Do not try to control Praxelis without expert assistance. Control effort that is poorly performed or not followed up can actually help spread the weed and worsen the problem (CRC 2003).

Chemical control: There are no herbicide products specifically registered for the control of Praxelis in Queensland. However, a permit held by the Department of Agriculture and Fisheries allows people generally to use some herbicide products to control Praxelis as an environmental weed in various situations (Qld DAF 2020)

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

Non-chemical control: Physical control: Hand pulling of small areas of Praxelis is not recommended. Mature seed can drop off and increase the area of infestation (Qld DAF 2020).

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

In tropical and subtropical regions Praxelis mainly flowers during the wetter months between November and May. However, a few flowers may be present on some plants year round. Seeds are formed and drop from the plant very quickly, mainly throughout summer and autumn. Most germination occurs following rainfall, but it can occur year round under suitable conditions (e.g. in gardens, irrigated pasture).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

Infestations have been recorded along the coast of northern Queensland from Townsville to Cairns, and on the Atherton Tablelands at Kuranda, Mareeba, Herberton and Malanda. Other scattered infestations exist in remote parts of Cape York Peninsula and the Torres Strait islands, originating from seeds in building and landscaping materials brought in from infested regions. In 2002 an infestation was discovered just north of Gympie, some 1200 km by road from Townsville and only 160 km north of Brisbane (CRC 2003, ATH 2020).

Where does it originate?

A native of subtropical South America (southern Brazil, Venezuela, Bolivia, northern Argentina) (CRC 2003). It is also an invasive weed in China (Waterhouse 2003).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Praxelis clematidea

Other scientific names (synonyms)?

  • Eupatorium catarium Veldk.
  • Eupatorium clematideum Less. ex Baker
  • Eupatorium clematideum Griseb.

Other Management Resources

Blackberry – a community-driven approach in Victoria

Blackberry the weed (Rubus fruticosus aggregate) was first introduced to Australia by European settlers in the mid-1800s as a fruit. It was recognised as a weed by mid-1880s. Blackberry is a serious issue across Australia. It is estimated that blackberry infests approximately 8.8 million hectares of land at an estimated cost of $103 million in annual control and production losses.

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