Weed Identification

Australia > > Parthenium Weed

Parthenium Weed

Parthenium hysterophorus

THIS PLANT HAS BEEN DECLARED A WEED OF NATIONAL SIGNIFICANCE

Alternative Name(s): Bitter Weed, Feverfew, False Ragweed, Whitetop.

Family: Asteraceae.

Form: Herb

Origin: Native to tropical America.

Flowers/Seedhead: Flowers: In a branched panicle. Flowers most of year in tropics and subtropics.

Description: Erect annual to about 1.5 m tall. Seed black, 2–3.5 mm long, topped with membranous white scales about 0.5 mm long.

Distinguishing features: Distinguished by flowers in heads about 4 mm wide with 5 small petal-like ray florets (see photo), deeply lobed leaves at the rosette stage, and single stemmed habit of the mature plant and lobed leaves covered in fine hair.

Dispersal: Seeds carried by water and wind. Transported in hay, machinery, mud and by stock.

Confused With: Ragweeds Ambrosia spp., before flowering.


Mature plants are normally
about 1 m tall

Notes: Can germinate, flower, and set seed in 4–6 weeks. Flowering continues until the plant dies. Seeds are viable for up to about 2 years. Colonises roadsides, fallow and overgrazed land. Generally shunned by stock; if eaten it will taint meat and milk. Prolonged contact can cause asthma, acute dermatitis and respiratory problems in humans.

References:

    Noxious Weeds of Australia. W. Parsons and E. Cuthbertson, 1992, pages 292–296. The Biology of Australian Weeds. F. Panetta et al. (eds), Vol. 2, 1998, pages 157–176.

Web References: Search Australian web sites for further information on this weed.

Ribbed stem
Flowers with 5 small petal-like ray
florets & leaf
Juvenile with deeply
lobed leaves

This weed has been included in the WEEDeck field guide as card H02

More information about WEEDeck is available from Sainty & Associates Pty. Ltd.

 

Australia > > Parthenium Weed

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