Name:
Parthenium
Botanical Name:
Parthenium hysterophorus
Description
Parthenium Weed (Parthenium hysterophorus) is an aromatic, annual herb initially forming a basal rosette of leaves but then becoming much-branched and usually about 0.5-1.5 m tall. In favourable situations it can grow to 2 m tall. It has divided, softly hairy leaves arranged alternately along the stem, decreasing in size towards the top of the plant. The flowers heads are white and borne in loose clusters on the tips of branches. The wedge-shaped seeds (known as achenes cypselas) are black at maturity, about 2 mm long, and end in 2 broad, membranous white scales about 0.5 mm long.
For further information and assistance with identification of Parthenium Weed contact the herbarium in your state or territory.
Distribution:
Within Australia, Parthenium Weed has been recorded from Queensland, New South Wales and the Northern Territory. It is widespread and seemingly entrenched in central Queensland. Around 2000 the core area of infestation in the central highlands of Queensland was estimated to be 8.2 million hectares. Scattered infestations also occur in Queensland from Cook shire in the north to Longreach in the west and south to the border towns of Goondiwindi and Mungindi.
In New South Wales, sporadic infestations have been reported from as far south as Deniliquin and Jerilderie. However, in a report in 2001 it was noted that the extent of Parthenium Weed in the state had been significantly reduced since its introduction in 1982 and in 2004 it was recorded that Parthenium Weed has been prevented from establishing in New South Wales, although it is also evident that more outbreaks are inevitable.
From published records the extent to which Parthenium Weed has been noted in the Northern Territory is unclear, but reports are few.It was reported that the original infestation of 1977 at Elsey Creek, in the Mataranka district, had almost been eradicated. At that time no other infestations were known. Since then, the Elsey population has been eradicated and sporadic outbreaks on rural blocks in the Katherine area have also been successfully treated. Seemingly, two outbreaks in the Northern Territory Gulf country in 1991 - one near Borroloola and the other at Limmen Bight - have also been satisfactorily dealt with.
Habit:
Herb
Key points:
- Parthenium Weed (Parthenium hysterophorus) is a prolific setter of seed, an average-sized plant producing about 15,000 seed; with a significant portion of buried seed remaining viable for six or more years.
- It invades grazing land and summer cropping areas as well as disturbed native vegetation, its aggressiveness partly due to an allelopathic effect on other plants.
- It favours cracking clay soils.
- The species can cause respiratory problems and severe dermatitis in humans.
- It taints meat and milk of livestock.
How it spreads:
Parthenium Weed is a prolific seeder. Soil seed-bank studies in Australia reveal as many as 400 million seeds per hectare. The seed can be dispersed by both water, with significant spread along waterways noted in central Queensland, and by wind. Similarly, they can be spread by livestock and other animals in the hair or mud attached to their bodies.
Long-distance dispersal can take place by the movement of contaminated passenger vehicles, farm machinery, livestock, stock feed and pasture seed. In Queensland there is a legal requirement for suppliers of stock, machinery and other products to sign a declaration whether or not the material is clean of seed. Legislation is also in place which requires agricultural machinery moving from Queensland to New South Wales to be inspected at the border, a process considered to have greatly reduced the risk of further introductions into the latter state.
Where it grows:
Parthenium Weed can be prolific in disturbed situations, both natural and unnatural, and has a marked preference for highly fertile, black, alkaline, cracking clay soils but does grow on other soils, albeit not usually as vigorously. Climatically it has a preference for areas with an annual summer rainfall greater than 500 mm. Flooded country is also very prone to Parthenium Weed infestations.
Flower colour:
White
Distribution map:
Impacts:
Parthenium Weed is a Weed of National Significance. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.
Parthenium Weed is a major problem in rangeland and summer-cropping areas of Queensland, costing farmers and graziers over $22 million a year in reduced production and increased management costs. It readily colonises disturbed and heavily stocked areas, reduces both pasture establishment and potential, and invades native vegetation. In Queensland it threatens biodiversity in the Einasleigh Uplands bioregion and native grassland in the central highlands. It is somewhat toxic to livestock and taints meat and milk. In people, repeated contact with plants can produce allergic dermatitis, while in others the pollen may cause hay fever and asthma.
Origin:
Parthenium Weed was originally described and formally named from material gathered in Jamaica. The species is native to the Caribbean region, and according to some reports also other regions of central America, Mexico and parts of South America.
It is considered to be an introduction to the United Statesand introduced to many other regions, including Israel, Kenya, South Africa, Madagascar, Mauritius, Mozambique, the Seychelles, India, Bangladesh, Nepal, parts of China, Vietnam, Taiwan, many Pacific island (including Hawaii, New Caledonia, New Guinea & Tahiti) and Australia.
History:
Parthenium Weed was first recorded in Australia at Toogoolawah, Queensland in 1955 and it is considered that it was probably introduced during World War II with American aircraft landing at a local airstrip. It was subsequently discovered in 1964 (or perhaps earlier) north of Clermont, this time introduced as a contaminant of pasture grass obtained from Texas (United States). It spread rapidly from this locality following good winter rains in 1973. It was first recorded in the Northern Territory in 1977 and in New South Wales in 1982.
