Weed Identification

Australia > > Annual Ragweed

Annual Ragweed

Ambrosia artemisiifolia

Alternative Name(s): Common Ragweed

Family: Asteraceae.

Form: Herb

Origin: Native of North America.

Flowers/Seedhead: Male inflorescence a terminal spike to 15 cm long. Male flowers greenish-yellow, 10100 per head. Female flowers one per head. Flowers late summer and autumn.

Description: Erect annual herb to 2 (rarely to 3.5) m high. Leaves grey-green, hairy, variable, lower leaves ovate to lanceolate in outline, with blade to 16 cm long, 17 cm wide on a stalk to 10 (usually13) cm long; finely divided; upper leaves sometimes without lobes and often almost without a stalk.

Distinguishing features: Distinguished by annual shallow-rooted growth; lower leaves twice divided (bipinnate); male flowers in drooping cone-shaped clusters in spikes above female flowers which are hidden in leaf axils; 'seeds' hairless or sparsely hairy, with a ring of 47 spines each about 1 mm long.

Dispersal: Spread by seed attached to animals or in mud.

Confused With: Other Ambrosia species, see taxonomic texts for detailed distinguishing features. May also be confused with Chinese Wormwood, Artemisia verlotiorum, but Artemisia species have flowerheads that contain clusters of flowers of both sexes.

Many branched stems with erect flower
spikes Florida, USA

Notes: Weed of roadsides, wastelands and occasionally cultivation. Major cause of allergy with pollen causing flu-like symptoms; contact with the plant can also cause skin allergies. The stem-galling moth, Epiblema strenuana, introduced for control of Parthenium Weed, Parthenium hysterophorus, reduces Annual Ragweed populations in warmer areas.


    Noxious Weeds of Australia. W. Parsons and E. Cuthbertson, 1992, pages 245248.

Spikes of hooded male flowers & single female
flowers at leaf bases, Nimbin, NSW, April

Immature fruit with spines


This weed has been included in the WEEDeck field guide as card H13

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


Australia > > Annual Ragweed


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