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Scientific Name
Synonyms
Common Names
Family
Origin
Naturalised Distribution
Habitat
Distinguishing Features
Habit
Stems and Leaves
Flowers and Fruit
Reproduction and Dispersal
Impacts
Other Impacts
Control 
Similar Species
Legislation
Management
Sources
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Click on images to enlarge


infestation (Photo: Sheldon Navie)


habit prior to flowering (Photo: Sheldon Navie)


habit in flower (Photo: Sheldon Navie)


hairy rounded stem (Photo: Sheldon Navie)


highly-divided and fern-like lower leaf (Photo: Sheldon Navie)


smaller, alternately arranged, and less-divided upper leaves (Photo: Sheldon Navie)


young flower clusters (Photo: Sheldon Navie)


male flower-heads in elongated clusters (Photo: Sheldon Navie)


female flower-heads and fruit, left, and old male flower-heads, right (Photo: Sheldon Navie)


close-up of seeds (Photo: Steve Hurst at USDA PLANTS Database)


seedling (Photo: Sheldon Navie)


young plant forming a rosette of oppositely arranged leaves (Photo: Sheldon Navie)


adult Zygogramma bicolorata beetles on annual ragweed leaves (Photo: Sheldon Navie)


larvae of the stem-galling moth Epiblema strenuana in an annual ragweed stem (Photo: Sheldon Navie)

Annual ragweed
Ambrosia artemisiifolia

Scientific Name

Ambrosia artemisiifolia L.

Synonyms

Ambrosia diversifolia (Piper) Rydb.
Ambrosia elatior L.
Ambrosia media Rydb.
Ambrosia monophylla (Walt.) Rydb.

Common Names

ambrosia, American wormwood, annual bur-sage, annual ragweed, asthma plant, bastard wormwood, bitterweed, black weed, blackweed, carrot weed, carrot-weed, common ragweed, hay fever weed, hay-fever weed, hog weed, hogbrake, hog-weed, hogweed, horseweed, low ragweed, mayweed, ragweed, Roman bitterweed, Roman wormweed, Roman wormwood, short ragweed, small ragweed, Stalin weed, stammerweed, stammerwort, stickweed, tassel weed, wild tansy

Family

Asteraceae (Queensland, New South Wales, the ACT, Victoria, Tasmania, Western Australia and the Northern Territory)
Compositae (South Australia)

Origin

Native to large parts of North America (i.e. in southern Canada and throughout most of the USA).

Naturalised Distribution

Widely naturalised in eastern Australia and also present in southern Australia. It is most common and widespread in eastern Queensland and the coastal and sub-coastal districts of central and northern New South Wales (particularly in south-eastern Queensland and north-eastern New South Wales). Also occasionally naturalised in some parts of Victoria.

Naturalised in many other parts of the world, including China and Hawaii.

Habitat

This species is mostly found in warmer temperate and sub-tropical environments. It is a common weed of pastures, open woodlands, roadsides, disturbed sites, waste areas, creek banks and riparian vegetation, and is occasionally also found growing in cultivation.

Distinguishing Features

Habit

A short-lived (i.e. annual) herbaceous plant with an upright (i.e. erect) habit, growing up to 2 m tall.

Stems and Leaves

This plant forms a basal rosette of leaves during the early stages of growth. The much-branched, upright (i.e. erect), stems are rounded in cross-section(i.e. cylindrical) and reddish or brownish-green in colour. These stems vary from being almost hairless (i.e. sub-glabrous) to roughly hairy (i.e. hirsute).

The leaves are oppositely arranged at the base of the plant, but are alternately arranged further up the stems. The leaf blades (1-16 cm long and 1-7 cm wide) are deeply divided (i.e. pinnatifid to bi-pinnatifid) and fern-like in appearance. They are borne on leaf stalks (i.e. petioles) usually about 1-3 cm long (occasionally up to 10 cm long). The uppermost leaves are usually much reduced in size and less divided than the lower leaves. All leaves are usually covered in hairs (i.e. pubescent), particularly on their undersides, and these hairs may be long and spreading or short and soft.

Flowers and Fruit

Separate male and female (i.e. unisexual) flower-heads are formed on different parts of the same plant (i.e. this species is monoecious). The male (i.e. staminate) flower-heads outnumber the female (i.e. pistillate) flower-heads and droop from branching spike-like flower clusters (up to 20 cm long) that are borne at the tips of the stems. These male flower-heads are small, hemispherical in shape, and either cream, yellowish or pale green in colour. The female flower-heads are less conspicuous and consist of a single tiny flower (i.e. floret). The base of these flower-heads (i.e. the involucre) is saucer shaped with 5-7 small bristle-like spines (each 3-5 mm long). These female flower-heads are held upright and borne singly in the forks (i.e. axils) of the uppermost leaves (i.e. below the male flower-heads). Flowering occurs mostly during summer, autumn and early winter.

The fruit is a small brown or blackish achene (2-5 mm long) that is top-shaped (i.e. turbinate) and contains a single seed. These fruit become woody as they mature and have a pointed beak (1-2 mm long) and a ring of four to eight small blunt spines (each less than 1 mm long).

Reproduction and Dispersal

This plant reproduces mainly by seeds. The seeds are spread by animals, water, the movement of soil, and in contaminated agricultural produce (e.g. fodder and pasture seed).

Impacts

Annual ragweed (Ambrosia artemisiifolia) is mainly seen as a weed of disturbed sites and pastures in eastern Australia. However, it is also regarded as an environmental weed in some parts of New South Wales and Queensland and is listed as a priority environmental weed in at least one Natural Resource Management region. This species can become very abundant in overgrazed natural pastures, as well as in riparian areas (i.e. along creek banks, on floodplains, and on sandy creek beds), where it replaces native species.

In New South Wales, annual ragweed (Ambrosia artemisiifolia) is mainly a problem in coastal districts north of Sydney and it appears on several environmental weed lists in this region (i.e. it is an alert weed in the Sydney North region, is on the NSW North Coast environmental weed survey list, and is listed as an environmental weed in Byron Shire). It has also been recorded in conservation areas in north-eastern New South Wales (i.e. Billinudgel Nature Reserve) and south-eastern Queensland (i.e. Tugun Hill Conservation Area). Dense stands of this and other weed species are also seen as a threat to the integrity of remnant littoral rainforests in the coastal regions of New South Wales, and these rainforests are regarded as an endangered ecological community in this state.

Annual ragweed (Ambrosia artemisiifolia) is also considered to be an invasive species in Europe (e.g. France and Switzerland) and parts of Asia, although it is not an extremely aggressive species. It also displaces native vegetation in these countries, especially after disturbance events which put competitive pressures on the native flora.

A stem-galling moth (i.e. Epiblema strenuana) and a leaf-feeding beetle (i.e. Zygogramma bicolorata), which were introduced as biological control agents of parthenium weed (Parthenium hysterophorus ), also attack annual ragweed (Ambrosia artemisiifolia) and may reduce its invasiveness in sub-tropical regions.

Other Impacts

Annual ragweed (Ambrosia artemisiifolia) is probably most well known because of the impacts it can have on human health. It produces copious amounts of wind-dispersed pollen in its male flower-heads. This wind-borne pollen causes severe allergic reactions in sensitive people, compounding health problems like hay fever and asthma, and causing skin irritations.

It invades weak pastures and can become particularly dense in pastures which are overgrazed, reducing their productivity. Annual ragweed (Ambrosia artemisiifolia) can also cause illness in livestock that ingest it and is a pest in orchards, vegetable crops and summer crops (e.g. sunflower and maize).

Control

Biosecurity Queensland Control Fact Sheet

Similar Species

Annual ragweed (Ambrosia artemisiifolia) is very similar to the other ragweeds (Ambrosia spp.) present in Australia, including burr ragweed (Ambrosia confertiflora), perennial ragweed (Ambrosia psilostachya) and lacy ragweed (Ambrosia tenuifolia). It is also very similar to parthenium weed (Parthenium hysterophorus ) when in the vegetative stage of growth. These species can be distinguished by the following differences:

Annual ragweed (Ambrosia artemisiifolia) may also be confused with some of the wormwoods (Artemisia spp.). However, these species have bisexual flowers in rounded flower-heads and they do not produce burr -like fruit.

Legislation

This species is declared under legislation in the following states and territories:

Management

For information on the management of this species see the following resources:

Sources

Anonymous (2002). A Global Compendium of Weeds. http://www.hear.org/gcw. Hawaiian Ecosystems at Risk Project and Department of Agriculture, Perth, Western Australia.

Anonymous (2006). Ambrosia artemisiifolia L., Asteraceae. Pacific Island Ecosystems at Risk (PIER): plant threats to Pacific ecosystems. http://www.hear.org/Pier/species/ambrosia_artemisiifolia.htm. Institute of Pacific Islands Forestry, Hawaii, USA.

Anonymous (2006). Annual ragweed: Ambrosia artemisiifolia. Natural Resources and Water Facts - pest series, PP7. The State of Queensland (Department of Natural Resources and Water), Brisbane, Queensland.

Anonymous (2006). Australia's Virtual Herbarium. http://www.anbg.gov.au/avh. Australian National Botanic Gardens, Environment Australia, Canberra, ACT.

Anonymous (2006). Declared Plants of Queensland. Natural Resources and Water Facts - pest series, PP1. The State of Queensland (Department of Natural Resources and Water), Brisbane, Queensland.

Anonymous (2006). Germplasm Resources Information Network (GRIN). http://www.ars-grin.gov/cgi-bin/npgs/html/index.pl. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA.

Anonymous (2007). Littoral Rainforest in the NSW North Coast, Sydney Basin and South East Corner Bioregions - endangered ecological community listing. http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Littoral_Rainforest_endangered. NSW National Parks and Wildlife Service, Department of Environment and Climate Change, New South Wales.

Anonymous (2007). NSW Department of Primary Industries. http://www.dpi.nsw.gov.au. NSW Department of Primary Industries, Orange, New South Wales.

Anonymous (2007). Weeds Australia. http://www.weeds.org.au. National Weeds Strategy Executive Committee, Launceston, Tasmania.

Auld, B.A. and Medd, R.W. (1996). Weeds: an illustrated botanical guide to weeds of Australia. Inkata Press, Sydney, New South Wales.

Bostock, P.D. and Holland, A.E. (2007). Census of the Queensland Flora 2007. Queensland Herbarium, Environmental Protection Agency (EPA), Brisbane, Queensland.

Crothers, M. (1993). Ragweed (Ambrosia spp). Ambrosia artemisiifolia L. (Annual Ragweed) Ambrosia psilostachya D.C. (Perennial or Western Ragweed). Agnote. Weeds Branch, Primary Industry and Fisheries, Northern Territory of Australia, Darwin, Northern Territory.

Friend, E. (1983). Queensland Weed Seeds. Queensland Department of Primary Industries, Brisbane, Queensland.

Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane, Queensland.

Lazarides, M., Cowley, K. and Hohnen, P. (1997). CSIRO Handbook of Australian Weeds. CSIRO Publishing, Collingwood, Victoria.

Murray, L. (1992). Ambrosia. In: Flora of New South Wales, Volume 3 (ed: G. Harden). New South Wales University Press, Kensington, New South Wales.

Navie, S.C. (2004). Declared Plants of Australia. CD-ROM. The University of Queensland, St. Lucia, Queensland.

Navie, S.C., Markwell, B., Playford, J. and Adkins, S.W. (2002). Suburban and Environmental Weeds: an interactive identification and information system. CD-ROM. The University of Queensland, St. Lucia, Queensland.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious Weeds of Australia. Inkata Press, Melbourne, Victoria.

Stanley, T.E. and Ross, E.M. (1986). Flora of South-eastern Queensland. Volume 2. Department of Primary Industries, Brisbane, Queensland.

Walsh, N.G. and Stajsic, V. (2007). A Census of the Vascular Plants of Victoria. Eighth Edition. National Herbarium of Victoria, South Yarra, Victoria.