Description
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 tearshaped 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 pappusbristles at the apex.
For further information and assistance with identification of Praxelis contact the herbarium in your state or territory.
Distribution:
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.
Habit:
Herb
Key points:
- Praxelis (Praxelis clematidea) spreads into new areas very quickly. Seed dispersal is aided by machinery and vehicles.
- 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.
- Prevention is the most cost-effective form of weed control. Keep uninfested areas free of Praxelis. Do not attempt control on your own.
How it spreads:
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.
Where it grows:
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.
Flower colour:
Blue
Distribution map:
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. Although only in the early stages of establishment, these weeds have the potential to seriously degrade Australia’s ecosystems. An invader of both disturbed and relatively undisturbed ecosystems, Praxelis could threaten, and significantly increase the costs of managing, such crops as bananas, other fruits and sugar cane. 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.
Origin:
A native of subtropical South America (southern Brazil, Venezuela, Bolivia, northern Argentina). It also an invasive weed in China.
