Preferred Scientific Name
- Onopordum acaulon L.
Preferred Common Name
- horse thistle
International Common Names
- English: stemless onopordon; stemless thistle
- Portuguese: cardo
Datasheet
Onopordum acaulon (horse thistle)
Index
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Top of pageSummary of Invasiveness
Top of pageOnopordum acaulon, stemless thistle, reduces the carrying capacity of the land it infests and seriously harms livestock that try to eat it, resulting in impaction and liver damage. A pest risk assessment finalized by APHIS (Lehtonen, 2004) ranked the weed with medium consequences of introduction and high likelihood of introduction resulting in a ranking of medium-high overall risk potential in the USA. O. acaulon was added to the Federal Noxious Weed List and seed list in 2010.
Taxonomic Tree
Top of page- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Onopordum
- Species: Onopordum acaulon
Description
Top of pageO. acaulon is nearly stemless, with the stalks rarely exceeding 10 cm in length. The short-stalked leaves are 15-38 cm long and deeply dissected into spine-toothed lobes and are narrow and oblong, grey or white-hairy on both surfaces. The flower heads are white or purple, and form at the centre of the basal rosettes of foliage (Everett, 1981). Seeds are grey-brown and about 4 mm long. They are four-sided, pitted and ridged lengthwise, with a pappus of cream-coloured barbed hairs about 25 mm long. In Australia, stemless thistles germinate from seed mainly in the autumn. Plants develop during winter into small rosettes, which grow rapidly in spring. They flower from October to November dying in summer. Some seeds germinate during winter and spring, but most of the resulting plants do not develop sufficiently to flower before dying. Under favourable conditions, some of these plants do survive and flower in the second summer. Reproduction is by seeds only.
Distribution
Top of pageStemless thistle is believed to have originated in northern Africa and southwestern Europe. It was introduced to Australia as an ornamental and as an agricultural contaminant. Since then, it has naturalized and become a major pest along roadsides and wastelands, and specifically in cultivated lands and pastures. Stemless thistle is not known to be present in the United States, but there is a high likelihood of its introduction. The plant thrives in warm temperate regions that receive less than 50 cm of annual precipitation. It would probably establish itself in the southwestern United States, including Texas, California and Arizona.
Distribution Table
Top of pageThe distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Last updated: 10 Feb 2022Habitat List
Top of page| Category | Sub-Category | Habitat | Presence | Status |
|---|---|---|---|---|
| Terrestrial | Managed | Cultivated / agricultural land | Principal habitat | |
| Terrestrial | Managed | Managed grasslands (grazing systems) | Principal habitat | |
| Terrestrial | Managed | Disturbed areas | Principal habitat | |
| Terrestrial | Managed | Rail / roadsides | Principal habitat | |
| Terrestrial | Natural / Semi-natural | Natural grasslands | Principal habitat | |
| Terrestrial | Natural / Semi-natural | Arid regions | Principal habitat |
Plant Trade
Top of page| Plant parts liable to carry the pest in trade/transport | Pest stages | Borne internally | Borne externally | Visibility of pest or symptoms |
|---|---|---|---|---|
| True seeds (inc. grain) | weeds/seeds | Yes |
Risk and Impact Factors
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Invasiveness
- Proved invasive outside its native range
- Negatively impacts animal health
- Competition - monopolizing resources
- Produces spines, thorns or burrs
Bibliography
Top of pageDepartment of Primary Industries (DPI). “Stemless thistle (Onopordum acaulon) (Nox).” Ministries of Agriculture and Energy and Resources for Victoria, Australia. Last updated 10 June 2009, accessed 12 June 2009. http://www.dpi.vic.gov.au/DPI/Vro/vrosite.nsf/pages/weeds_herbs_annual_stemless_thistle
Everett, Thomas H. 1981. The New York Botanical Garden Illustrated Encyclopedia of Horticulture Volume 3. General Publishing, Inc. New York & London.
USDA, ARS 2009. Germplasm Resources Information Network (http://www.ars-grin.gov/, 12 June 2009). 10300 Baltimore Blvd, Beltsville, MD 20705, USA.
Links to Websites
Top of page| Website | URL | Comment |
|---|---|---|
| GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway | https://doi.org/10.5061/dryad.m93f6 | Data source for updated system data added to species habitat list. |
Distribution Maps
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