Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Onopordum acanthium
(scotch thistle)



Onopordum acanthium (scotch thistle)


  • Last modified
  • 15 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Onopordum acanthium
  • Preferred Common Name
  • scotch thistle
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • O. acanthium is considered an important weed in Australia, Argentina, the USA and parts of Canada. In the USA it is a declared noxious weed in 12 states. In New Zealand, it is a minor weed of neglected areas in drier parts but has the potential to be...

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Onopordum acanthium (scotch thistle); flowers and stem. USA.
TitleFlowers and stem
CaptionOnopordum acanthium (scotch thistle); flowers and stem. USA.
Copyright©Bonnie Million/National Park Service/ - CC BY-NC 3.0 US
Onopordum acanthium (scotch thistle); flowers and stem. USA.
Flowers and stemOnopordum acanthium (scotch thistle); flowers and stem. USA.©Bonnie Million/National Park Service/ - CC BY-NC 3.0 US
Onopordum acanthium (scotch thistle); flowers. USA.
CaptionOnopordum acanthium (scotch thistle); flowers. USA.
Copyright©Bonnie Million/National Park Service/ - CC BY-NC 3.0 US
Onopordum acanthium (scotch thistle); flowers. USA.
FlowersOnopordum acanthium (scotch thistle); flowers. USA.©Bonnie Million/National Park Service/ - CC BY-NC 3.0 US
Onopordum acanthium (scotch thistle); habit. USA.
CaptionOnopordum acanthium (scotch thistle); habit. USA.
Copyright©Vince Belleci/ - CC BY 3.0 US
Onopordum acanthium (scotch thistle); habit. USA.
HabitOnopordum acanthium (scotch thistle); habit. USA.©Vince Belleci/ - CC BY 3.0 US
Onopordum acanthium (scotch thistle); leaves. USA.
CaptionOnopordum acanthium (scotch thistle); leaves. USA.
Copyright©Bonnie Million/National Park Service/ - CC BY-NC 3.0 US
Onopordum acanthium (scotch thistle); leaves. USA.
LeavesOnopordum acanthium (scotch thistle); leaves. USA.©Bonnie Million/National Park Service/ - CC BY-NC 3.0 US


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Preferred Scientific Name

  • Onopordum acanthium L.

Preferred Common Name

  • scotch thistle

Other Scientific Names

  • Acanos spina Scop.
  • Onopordum acanthifolium Gilib.

International Common Names

  • English: asses' thistle; Queen Mary's thistle; winged thistle
  • Spanish: alcachofa borriquera
  • French: onoporde cotonneuse
  • Russian: onopordum kolyuchii
  • Portuguese: acanto-bastardo

Local Common Names

  • Australia: heraldic thistle; woolly thistle
  • Australia/Tasmania: cotton thistle
  • Canada: onoporde acanthe
  • Czech Republic: ostropes trubil
  • Denmark: aeselfoder
  • Germany: Eseldistel
  • Italy: acanzio
  • Netherlands: wegdistel, witte
  • New Zealand: cotton thistle
  • Poland: poploch pospolity
  • Sweden: ulltistel
  • UK: cotton thistle
  • USA: cotton thistle; silver thistle

EPPO code

  • ONRAC (Onopordum acanthium)

Summary of Invasiveness

Top of page O. acanthium is considered an important weed in Australia, Argentina, the USA and parts of Canada. In the USA it is a declared noxious weed in 12 states. In New Zealand, it is a minor weed of neglected areas in drier parts but has the potential to become much more invasive. In India, it is occasionally weedy. In its native range, O. acanthium can be weedy on grazing lands and fallows in Spain, Turkey, Russia and the UK. It has the potential to compete with most species and displace them from their natural habitats. Since O. acanthium can tolerate adverse environmental conditions and adapt to different habits, it continues to spread and occupy new areas. High cypsela production, variation in cypsela dormancy, intermittent germination patterns and vigorous growth habit make this species a serious invader. It competes with other species in pastures, rangelands and agricultural fields and causes injury to livestock and wild animals. It is difficult to eradicate entirely from an area due to its strong cypsela dormancy and persistent soil seed banks.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Asterales
  •                         Family: Asteraceae
  •                             Genus: Onopordum
  •                                 Species: Onopordum acanthium

Notes on Taxonomy and Nomenclature

Top of page Onopordum is derived from the Greek 'onus' (ass) and 'porde' (flatulence), because of the belief that the plant produced flatulence in donkeys; acanthium is from the Latin 'acanos' (thistle), which was derived from the Greek 'acantho' (spiny) (Parsons and Cuthbertson, 2000). The accepted common name is Scotch thistle though the species is known by a large number of other names. The subspecies that have been reported for this species are O. acanthium subsp. acanthium, O. acanthium subsp. gautieri (Rouy) Franco, O. acanthium subsp. parnassicum (Boiss. & Heldr.) Nyman (Tutin et al., 1976), O. acanthium subsp. areneosotomentosum Rech.f. (Rechinger, 1979), O. acanthium subsp. ceretanum (Sen.) Ar. (Guinochet and Vilmorin, 1982) and O. acanthium subsp. gypsicola (Gonzalez-Sierra et al., 1992), and the variety O. acanthium var. alba Hort. (Michael, 1996).


Top of page O. acanthium is usually a monocarpic biennial, but under certain conditions it can be an annual or short-lived perennial (Hyde-Wyatt, 1968). The seedling has a very short hypocotyl and no epicotyl (Hyde-Wyatt and Morris, 1980). Rosettes that originated from autumn-emerged seedlings and experienced over-wintering may be very large, with leaves up to 90 cm long, 35 cm wide and 1.5 mm thick. The mature plant has a large and fleshy taproot. The stem of the flowering plant is yellowish-green, erect, branched, woody, ridged and with conspicuous spiny-margined wings. A mature plant grows up to 3 m in height. The leaves, with triangular lobes, are oblong in young plants and rectangular in older plants. The leaves and stems are usually covered with fine silvery-white hairs which give the plant a greyish appearance. Many flowers (florets) are borne on a flat and conical receptacle. The florets are bisexual and actinomorphic. The epigynous calyx consists of a pappus of awns. The corolla of five petals is sympetalous and tubular (Qaderi, 2002). The regular flower colour is purple, but white-flowered populations have also been reported (Danin, 1975). The capitula, 10-32 mm in diameter and 10-21 mm in height, are flat, solitary or in terminal clusters of two to seven with short spines on the bracts. Each capitulum (flower head) produces from 0 (if all aborted) to 400 achenes (strictly a 'cypsela' - an indehiscent dry fruit developed from a one-loculed, inferior ovary, with persistent calyx attached) (Qaderi, 2002). The achene develops from a fertilized anatropous ovule in which the funiculus is attached basally near the adjoining micropyle (Radford, 1986). The mature achene consists of a pericarp, a testa, a single layer of endosperm, and an embryo with an axis and two cotyledons. The achenes are oblong, 4.1-6.0 mm in length, 1.7-3.3 mm in width, 0.9-2.2 mm in depth and 4.0-18.7 mg in weight. They are deep brown to black and curved (from the periphery of the capitulum) to straight (from the centre of the capitulum). The pappus hairs are 4-10 mm long, yellowish at maturity, unequal in length and up to twice as long as the achenes (Qaderi, 2002).

Plant Type

Top of page Annual
Seed propagated


Top of page O. acanthium is a native of Europe, western and central Asia and Asia Minor (Young and Evans, 1969). It has a wide distribution range, from cool climates in Scandinavia (Boissier, 1875) and Siberia (Czerepanov, 1995) to warm areas such as North Africa (Harden, 1992), Australia (Jessop and Toelken, 1986) and southern USA (Young and Evans, 1969; Correll and Johnston, 1970; Keil and Turner, 1993).

Distribution Table

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The 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.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


AfghanistanPresentNativeRechinger, 1979
ArmeniaPresentNativeUSDA-ARS, 2003
AzerbaijanPresentNativeRechinger, 1979
-XinjiangPresentNativeFlora of China Editorial Committee, 2003
Georgia (Republic of)PresentNativeUSDA-ARS, 2003
IndiaPresent, few occurrencesParsons and Cuthbertson, 2000
-Jammu and KashmirPresentNativePolunin and Stainton, 1984
IranPresentNativeRechinger, 1979
IraqPresentNativeRechinger, 1979
JordanPresentNativeAbuharfeil et al., 2001
KazakhstanPresentNativeNevskii, 1929
KyrgyzstanPresentNativeNevskii, 1929
PakistanPresentNativeRechinger, 1979
TajikistanPresentNativeUSDA-ARS, 2003
TurkeyPresentNativeDanin, 1975; Holm et al., 1979
TurkmenistanPresentNativeRechinger, 1979
UzbekistanPresentNativeGigieniva and Umarov, 1981

North America

CanadaPresentIntroducedbefore 1867 Invasive Hubbert, 1867; Darbyshire, 2003
-AlbertaPresentIntroducedQaderi, 1998
-British ColumbiaPresentIntroduced Invasive Darbyshire, 2003
-New BrunswickPresentIntroducedDarbyshire, 2003
-Newfoundland and LabradorPresentIntroducedDarbyshire, 2003
-Nova ScotiaPresentIntroducedDarbyshire, 2003
-OntarioPresentIntroduced Invasive Darbyshire, 2003
-QuebecPresentIntroducedDarbyshire, 2003
-SaskatchewanPresentIntroducedThomas, 1976
USAPresentIntroducedlate 1800 Invasive Bentham and Hooker, 1904; Holm et al., 1979
-AlabamaPresentIntroducedUSDA-NRCS, 2002
-ArizonaPresentIntroduced Invasive Lehr, 1978
-CaliforniaPresentIntroduced Invasive Young and Evans, 1969; Keil and Turner, 1993
-ColoradoPresentIntroduced Invasive Weber and Wittmann, 1996
-ConnecticutPresentIntroducedMehrhoff et al., 2003
-DelawarePresentIntroducedUSDA-NRCS, 2002
-FloridaPresentIntroducedUSDA-NRCS, 2002
-IdahoPresentIntroduced Invasive Callihan and Miller, 1994; USDA-NRCS, 2002
-IllinoisRestricted distributionIntroducedJones and Fuller, 1955; USDA-NRCS, 2002
-IndianaRestricted distributionIntroducedDeam, 1940
-IowaPresent, few occurrencesIntroduced Not invasive Cratty, 1932; USDA-NRCS, 2002
-KansasPresentIntroducedGreat Plain Flora Association, 1986
-KentuckyPresentIntroducedUSDA-NRCS, 2002
-MarylandPresentIntroducedUSDA-NRCS, 2002
-MassachusettsPresentIntroducedUSDA-NRCS, 2002
-MichiganPresentIntroducedDeam, 1940; Britton and Brown, 1970
-MinnesotaPresentIntroducedUSDA-NRCS, 2002
-MissouriPresentIntroduced Invasive Steyermark, 1963
-MontanaPresentIntroducedTaylor, 1990
-NebraskaRestricted distributionIntroducedNebraska Department of Agriculture, 1979; McCarty et al., 1984
-NevadaPresentIntroduced Invasive Young and Evans, 1969
-New JerseyPresentIntroducedBritton and Brown, 1970; USDA-NRCS, 2002
-New MexicoPresentIntroduced Invasive Sivinski et al., 1994; USDA-NRCS, 2002
-New YorkPresentIntroduced Invasive USDA-NRCS, 2002
-OhioPresent, few occurrencesIntroducedFisher, 1988; USDA-NRCS, 2002
-OklahomaPresentIntroducedGreat Plain Flora Association, 1986
-OregonPresentIntroduced Invasive Peck, 1961; French et al., 1999
-PennsylvaniaPresentIntroducedBritton and Brown, 1970; USDA-NRCS, 2002
-Rhode IslandPresentIntroducedUSDA-NRCS, 2002
-South CarolinaPresentIntroducedBatson, 1975
-South DakotaPresentIntroducedUSDA-NRCS, 2002
-TexasPresentIntroducedCorrell and Johnston, 1970; USDA-NRCS, 2002
-UtahPresentIntroducedHolmgren and Andersen, 1970; USDA-NRCS, 2002
-VirginiaPresentIntroducedUSDA-NRCS, 2002
-WashingtonPresentIntroduced Invasive Gaines and Swan, 1972
-West VirginiaPresentIntroducedUSDA-NRCS, 2002
-WisconsinPresentIntroducedUSDA-NRCS, 2002
-WyomingPresentIntroduced Invasive Hilston, 1969

South America

ArgentinaPresentIntroduced Invasive Cabrera, 1971; Boeleke, 1986
ChilePresentIntroducedMatthei and Marticorena, 1990


AlbaniaPresentNativeTutin et al., 1976
AustriaPresentNativeTutin et al., 1976; Raabe, 1988
BelgiumPresentNativeTutin et al., 1976
BulgariaPresentNativeTutin et al., 1976
CroatiaPresentNativeWilliams and Hunyadi, 1987
Czech RepublicPresentNativeTutin et al., 1976
FinlandPresentNativeMoore and Frankton, 1974
FrancePresentNativeTutin et al., 1976; Guinochet and Vilmorin, 1982
-CorsicaPresentNativeTutin et al., 1976
GermanyPresentNativeTutin et al., 1976
GreecePresentNativeTutin et al., 1976
HungaryPresentNativeTutin et al., 1976
ItalyPresentNativeTutin et al., 1976
MoldovaPresentNativeUSDA-ARS, 2003
NetherlandsPresentNativeTutin et al., 1976
NorwayPresentNativeWilliams, 1982
PolandPresentNativeSzafer, 1966; Holm et al., 1979
PortugalPresentNativeTutin et al., 1976
RomaniaPresentNativeTutin et al., 1976
Russian FederationPresentNativeCzerepanov, 1995
-Central RussiaPresentNativeTutin et al., 1976
-Eastern SiberiaPresentNativeUSDA-ARS, 2003
-Russian Far EastPresentNativeZarubin et al., 1993
-Southern RussiaPresentNativeTutin et al., 1976
-Western SiberiaPresentNativeUSDA-ARS, 2003
SerbiaPresentNativeWilliams and Hunyadi, 1987
SlovakiaPresentNativeWilliams and Hunyadi, 1987
SpainPresentNativeTutin et al., 1976; Caballero, 1984
SwedenPresentNativeTutin et al., 1976
SwitzerlandPresentNativeTutin et al., 1976
UKPresentNativeTutin et al., 1976; Holm et al., 1979
UkrainePresentNativeVorobiov, 1960
Yugoslavia (former)PresentNativeTutin et al., 1976


AustraliaPresentIntroduced Invasive Willis, 1972; Holm et al., 1979
-New South WalesPresentIntroduced Invasive Groves et al., 1990
-South AustraliaPresentIntroducedAuld and Medd, 1987
-TasmaniaPresentIntroduced Invasive Curtis, 1963; Hyde-Wyatt and Morris, 1980
-VictoriaPresentIntroducedbefore 1850 Invasive Willis, 1972
-Western AustraliaPresentIntroducedGrieve and Blackall, 1975
New ZealandPresentIntroduced1880Holm et al., 1979; Webb et al., 1988

History of Introduction and Spread

Top of page O. acanthium has been introduced to other countries either accidentally or deliberately as an ornamental plant (Parsons and Cuthbertson, 2000). It was introduced to eastern USA in the late nineteenth century (Young and Evans, 1969) and in Canada, it has been naturalized for at least 135 years (Hubbert, 1867). This species showed weedy potential in Victoria, Australia by the 1850s and it is now well established throughout south-eastern Australia. In Tasmania, it spread rapidly in the 1950s and 1960s, but now its distribution has been reduced by more than 80% as the result of concerted campaigns against it (Parsons and Cuthbertson, 2000). O. acanthium has the potential to spread rapidly. For example, it was first located in Utah in 1963, and by 1981 it covered approximately 6070 ha in 17 counties and by 1989, it covered more than 22,540 ha in 22 counties (Dewey, 1991).

Risk of Introduction

Top of page It is possible that O. acanthium spreads to new areas as a result of accidental transportation of contaminated agricultural products such as crop seeds, or deliberate introduction of achenes for producing ornamental plants. In the USA, achenes of this species are sold, each package containing 100 achenes for US$2.65 (Lindley, 2003) or flowering plants are sold in Canada for C$7.00.


Top of page O. acanthium occurs commonly in wastelands, pastures, fields, rangelands, field margins, gravelly riverbanks and well-drained sandy or gravelly soils (Moore and Frankton, 1974; Piper, 1984; Dewey, 1991). In Europe, it is well established in continental areas with summer-dry climates (Mucina, 1989). In western USA, it infests wet meadows and pastures (Hooper et al., 1970). Temperature and moisture, rather than soil nutrient concentrations, determine the ecological performance of Onopordum species (Austin et al., 1985). In its native range, especially in Europe, O. acanthium tends to colonize disturbed pastures, where it is considered a weak competitor that needs regeneration gaps to develop and maintain stands (Mucina, 1989). In Australia, it occurs as a competitive weed of pastures mostly in southeast winter rainfall areas with 500-850 mm annual rainfall, but does not grow well on waterlogged soils (Parsons and Cuthbertson, 2000). The density and vigour of this species vary from year to year, probably because of climatic conditions, but this is not well understood (Michael, 1968).

Habitat List

Top of page
Cultivated / agricultural land Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details Harmful (pest or invasive)
Managed grasslands (grazing systems) Present, no further details Harmful (pest or invasive)
Rail / roadsides Present, no further details Harmful (pest or invasive)
Urban / peri-urban areas Present, no further details Harmful (pest or invasive)
Natural grasslands Present, no further details Harmful (pest or invasive)
Riverbanks Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top of page O. acanthium has been found in agricultural fields and causes problems in infested areas (Parsons, 1973; Smith et al., 1999; Qaderi et al., 2002). It competes with cereal crops in northern California, USA (Parsons and Cuthbertson, 2000).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Poaceae (grasses)PoaceaeOther
Triticum aestivum (wheat)PoaceaeMain

Growth Stages

Top of page Pre-emergence, Seedling stage, Vegetative growing stage

Biology and Ecology

Top of page Genetics

The chromosome number for O. acanthium is 2n=34 (Moore and Frankton, 1962; Podlech and Dieterle, 1969) and some other thistles belonging to the genus Cirsium and Silybum share this number (Moore and Frankton, 1974). Natural and artificial hybrids have been recognized. In Australia, natural hybridization can occur between O. acanthium and Illyrian thistle (O. illyricum) and it is difficult to separate hybrids from pure lines (Cavers et al., 1995; Michael, 1996). The correct name for the above hybrid is Onopordum x beckianum John (Sutory, 2001). Also, hybrid populations with O. tauricum Willd. occur in southern France (Danin, 1975). In Bulgaria, Georgieva et al. (1973) crossed O. acanthium with Helianthus annuus and found that the new form kept its type up to the twelfth generation, and the newly-obtained form could be crossed with H. annuus, but not with O. acanthium.

Physiology and Phenology

Some achenes of O. acanthium germinate as soon as they reach the soil in late summer or early autumn if adequate germination conditions are met. Before the onset of winter, the resulting seedlings form sizable rosettes. Spring-germinating plants are often larger than autumn-germinating plants to ensure that they flower in the next year. The following year, bolting rosettes flower, set achenes and then die. If achenes do not germinate soon after dispersal, they are incorporated into seed banks and over-winter in a dormant state. The next year, they may germinate in spring or early summer, remain in the rosette stage until the summer of the following year, then bolt, flower, set achenes and die. These two kinds of plants are winter annuals and biennials, respectively. If flowering plants are damaged, by ineffective cutting, cultivation or herbicides, they may produce some achenes but then become short-lived perennials by producing regrowth that will bolt in the following year, set achenes and then die (Qaderi, 1998).

Achenes of O. acanthium have a wide range of germination responses. Some achenes may germinate in the autumn shortly after dispersal (Qaderi and Cavers, 2000) while others may remain dormant for at least 40 years in the soil (Toole and Brown, 1946). Achenes can differ greatly in dormancy from different mother plants within a population (Pérez-García, 1993) and from different capitula within a plant (Meier, 1995). Scifres and McCarty (1969) reported that achenes of O. acanthium contain a water-soluble germination inhibitor and are sensitive to light quality. Young and Evans (1972) declared that this sensitivity to light quality is governed by phytochrome, and that both the soluble inhibitor and the sensitivity to light quality apparently function in the embryo and not in the achene coat. A water-soluble aromatic nitrogenous compound that exhibited inhibitory effects has been recently characterized (Qaderi et al., 2003b). Various secondary metabolites including phenolics, anthocyanins, flavonoids, sesquiterpenoids and amino acids have been extracted from this species (Glasby, 1991). Since O. acanthium is found in the dry habitats or in well drained soils, it shows an increase in achene germination after maturation under high temperatures or dry storage, and exhibits intermittent germination after maturation under cool field conditions (Qaderi and Cavers, 2000; Qaderi et al., 2003a).

Reproductive Biology

O. acanthium flowers from late June to October in the northern hemisphere (Qaderi, 1998) and from November to February in the southern hemisphere (Hyde-Wyatt, 1968; Webb et al., 1988). Ovule fertilization occurs by self- or cross-pollination that can be accomplished by wind or insects. Insect pollinators identified in Canada include bees (Andrena spp., Apis mellifera, Augochloropsis spp., Bombus bimaculatus, B. impatience, B. vagans), wasps (Cerceris spp.) and flies (e.g., Eristalis tenax) (Qaderi, 1998). O. acanthium reproduces almost entirely by achenes and, rarely, regeneration may occur from root systems (Qaderi, 1998). Depending on size, a single O. acanthium plant can produce from 100 to 50,000 achenes (Qaderi et al., 2002). After maturation, achenes are released from the parent plant although some are retained in the capitulum for a few weeks or months. Achenes can be dispersed by water, wind, wildlife, livestock and human activities (Hyde-Wyatt and Morris, 1980; Beck, 1999).

Environmental Requirements

O. acanthium is generally a species of open habitats with full sun or light shade (Bremness, 1989). This species is particularly common in highly fertile soils associated with pasture improvement (Auld and Medd, 1987). It also occurs in crops grown in land that has previously been under improved pasture. It is not normally found in native or unimproved pasture or in bush country (Hyde-Wyatt and Morris, 1980). It grows in soils with different textures (light, medium and heavy) and with wide pH ranges, from neutral to alkaline (Stewart and James, 1969; Qaderi, 1998), but requires rich loam to reach maximum height (Bremness, 1989). Over-wintering is required for bolting of rosettes and germination of some dormant achenes (Qaderi, 1998).


O. acanthium can also be abundant in dry pastures, fields and rangelands (Dewey, 1991). In the USA, it is often associated with plant communities dominated by the annual weedy grass Bromus tectorum (Beck, 1999). O. acanthium served as host for 30 species of insects (Coleoptera, Diptera and Hymenoptera) in 17 families that were found in association with a aphid colony (Brachycaudus cardui) in Ontario, Canada. These insects include feeders on honeydew, predators and parasites of aphids, and wasps that use aphids for nest provision (Judd, 1978). O. acanthium was host for the knapweed nematode Subanguina picridis (Watson, 1986).

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
0 0 0 0

Air Temperature

Top of page
Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) -24
Mean annual temperature (ºC) 2 15
Mean maximum temperature of hottest month (ºC) 14 29
Mean minimum temperature of coldest month (ºC) -12 2


Top of page
ParameterLower limitUpper limitDescription
Dry season duration12number of consecutive months with <40 mm rainfall
Mean annual rainfall5002000mm; lower/upper limits

Rainfall Regime

Top of page Uniform

Soil Tolerances

Top of page

Soil drainage

  • free
  • impeded

Soil reaction

  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • shallow

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Botanophila spinosa Herbivore Growing point
Larinus latus Herbivore Inflorescence/Seeds
Lixus cardui Herbivore Stems
Tephritis postica Herbivore Seeds
Terellia lappae Herbivore Inflorescence/Seeds
Trichosirocalus briesei Herbivore Growing point

Notes on Natural Enemies

Top of page Briese (1989) listed 25 species as natural enemies of O. acanthium, collected in the tablelands of New South Wales, Australia including insects (eight Lepidoptera, nine Hemiptera, one Coleoptera, one Diptera and one Thysanoptera;), two Acarina mites and one mollusc species. There was little or no damage from Hemiptera or Thysanoptera. These organisms were polyphagous and most of them were introduced species. In their native habitats, O. acanthium plants have been attacked and eaten by Trichosirocalus briesei (Briese et al., 2002), Botanophila spinosa (Vitou et al., 2001), Lixus cradui (Briese, 1996b), Cerajocera lappae (Basov, 1996) and Oxypteron schawerdai (King, 2001). These insects are being collected and introduced as biocontrol agents (see Biological Control section). No fungal pathogens have been reported attacking O. acanthium.

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

The only significant method of dispersal is by achenes, each of which is equipped with a stout pappus. Compared to other thistles, O. acanthium has a poorly developed pappus and achenes are not readily wind-borne. However, parts of the weed are easily dispersed by autumn or winter gales (Hyde-Wyatt and Morris, 1980; Qaderi, 1998).

Vector Transmission (Biotic)

Achenes can be entrapped in fleece or pass unharmed through the digestive tracts of sheep and possibly birds (Hyde-Wyatt and Morris, 1980). In Germany, increasing human activities enhanced the spread of ruderal species, such as O. acanthium, into areas outside their centres of origin (Weinert and Hellwig, 1987).

Agricultural Practices

There is some local spread of roots by cultivation equipment, as parts of the root system can be established in areas where suitable growth conditions are available (Hyde-Wyatt and Morris, 1980). Achenes can be moved long distances by attachment to vehicles and farm machinery.

Accidental Introduction

Achenes can be moved long distances in soil and gravel used for construction purposes (Qaderi and Cavers, 2000), O. acanthium achenes can contaminate crop seeds, and flowering plants may contaminate hay, which serves as accidental pathways for the introduction of this weed to new places (Parsons and Cuthbertson, 2000). Achenes have been intercepted in feed wheat and on sheep imported into Tasmania, Australia (Hyde-Wyatt and Morris, 1980).

Intentional Introduction

O. acanthium was probably introduced deliberately as an ornamental plant or because of other human uses (Michael, 1968). Flowering plants were seen for sale very recently in markets in Victoria, Canada, indicating that this continues to be a possible pathway for further spread.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Land vehiclesTransport vehicles and farm machinery Yes
Soil, sand and gravelWater Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Flowers/Inflorescences/Cones/Calyx seeds
Fruits (inc. pods) seeds
Growing medium accompanying plants seeds
True seeds (inc. grain) seeds
Plant parts not known to carry the pest in trade/transport
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches

Impact Summary

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Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production Negative
Environment (generally) Negative
Fisheries / aquaculture None
Forestry production None
Human health None
Livestock production Negative
Native fauna None
Native flora Negative
Rare/protected species None
Tourism Negative
Trade/international relations None
Transport/travel None


Top of page O. acanthium, with its intermittent germination and its prickly stem and leaves at maturity, causes problems for agricultural products, poultry and other livestock farms (Hooper et al., 1970; Auld et al., 1979; Wheatley, 1981). Hooper et al. (1970) stated that infestation of O. acanthium in northern California, USA, caused annual losses to ranchers of US$25.20/ha in wet meadows, US$16.60/ha in wheatgrass stands and US$8.40/ha in downy brome (Bromus tectorum-dominated) rangelands. In Australia, O. acanthium and O. illyricum are considered to be the worst and most costly weeds of the genus Onopordum. These two thistles form problem infestations in 57% of the counties in New South Wales with infestations mainly in southern and central tablelands (Briese, 1988) and the area infested is almost 1.1 million ha (Briese et al., 1990). The median annual cost of control, including labour, was as high as $A50/ha (Briese, 1996a) and the annual cost was estimated to be $A15-20 million in 1987. They are considered to be gradually spreading and are difficult and expensive to control by herbicides, particularly as they are resistant to cheap and mild hormonal herbicides such as 2,4-D and MCPA. If farmers want to eradicate O. acanthium from their lands they need to use more potent and expensive herbicides but these can also destroy valuable pasture species (Davidson, 1990). O. acanthium can act as a living fence, limiting access to grazing and water (Hyde-Wyatt, 1968; Hooper et al., 1970; Sindel, 1991). It also causes both wool flaw and injury to animals (Auld et al., 1979).

Environmental Impact

Top of page Its rapid growth and large size reduce available light for smaller plants and reduce other needed resources which may impact biodiversity (Sindel, 1991; Parsons and Cuthbertson, 2000).

Impact: Biodiversity

Top of page O. acanthium can form a dense monocultural stand, and if so, can eliminate clovers and desirable grasses (Hyde-Wyatt, 1968). It also competes with other plants in the natural environment and may displace, partially or completely, native plants from the area and threaten biodiversity (Beck, 1999). In the national Elk Refuge, Wyoming, USA, supplemental feeding of elks (Cervus elaphus) caused them to reduce tree and shrub cover, limit regeneration and render areas prone to exotic plant invasion including that of O. acanthium (Matson, 2000). In areas prone to sporadic natural fires, dormant achenes of this species will be triggered to germinate and produce vigorous seedlings which have the potential to rapidly take over gaps and exclude some previously existing species (Qaderi and Cavers, 2003).

Social Impact

Top of page O. acanthium, with its prickly stem, leaves and flower heads, can be harmful to man when contact is made with the mature plant or rosette. Dense infestations may prevent access to areas they border (Beck, 1999) and large plants along roadsides cause poor visibility which may present a hazard. Frequent occurrence of O. acanthium can be a problem in public parks (Hamilton, 1943) and when they occur in lawns, plants may cause problems to children or adults who contact them accidentally. A single O. acanthium is imposing enough, but an entire colony can ruin a pasture or destroy a park or campsite.

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Highly mobile locally
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts agriculture
  • Negatively impacts animal health
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
  • Produces spines, thorns or burrs
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally deliberately
  • Difficult/costly to control


Top of page First-year roots and young shoots of O. acanthium have been used as a vegetable in southern Europe (Moore and Frankton, 1974). After the outer bracts are removed, immature flower heads can be boiled or steamed and served with butter. Young stems are eaten raw with oil and vinegar or steamed and eaten hot after blanching and peeling. Achenes were formerly used to produce oil for cooking and lighting and the white hairs of leaves and stems were collected as pillow stuffing (Steyermark, 1963; Bremness, 1989). The pappus hairs have been woven into 'thistle cloth' (Moore and Frankton, 1974). It also had medicinal values, with the juice from leaves used to treat skin rashes, ulcers, rickets, nervous disorders and cancer, and root decoctions can reduce mucus discharges (Bremness, 1989). An aqueous extract from stem and leaves, which has been tested recently against tumour cells, showed intermediate augmentation with over 38% cytotoxicity (Abuharfeil et al., 2001). The whole plant forms a striking decorative feature in gardens and is widely valued as an ornamental species (Haughton, 1978).

Similarities to Other Species/Conditions

Top of page O. acanthium is similar to the genus Cirsium, but is distinguished by the fleshy receptacle that contains many honeycomb-like cells, each containing one ovary (Moore and Frankton, 1974). It is distinguished from other thistles by the very dense, white woolly covering on stems and leaves (Alex, 1992).

Prevention and Control

Top of page Cultural Control

The ability of thistles to invade pastures can be changed by grazing management (Sindel, 1991), primarily by changing the competitiveness of desirable pasture species (Sindel, 1996). Establishing and maintaining dense, vigorous, competitive pasture can effectively prevent O. acanthium establishment. Stocking pastures is an essential step in thistle control. Sheep, goats and horses, but not cattle, have a significant effect on thistles in the early stages of infestation when they eat young thistle plants (Wheatley, 1981). In a study, J. Leigh (in Davidson, 1990) showed that goats, which have a reputation for eating everything, ignored the leaves of O. acanthium, but they ate all the capitula (flower heads) and thus completely prevented seed dispersal from mature plants. Competition from deep-rooted perennial pasture grasses, such as Phalaris aquatica, can control O. acanthium, given at least 5-8 years continuous pasture (Michael, 1968).

Mechanical Control

A study has shown that in pastures previously given weed control treatments, cultivation and cropping was a successful control method. Small infestations can be eradicated by digging. After first flowering, mowing and slashing appears to be useful but were not very effective due to variation in cypsela maturity. Mowing will not kill the plant but will lessen the seed production by preventing seed heads from maturing (Qaderi, 1998). For total kill, plants must be cut off below the soil surface and no leaves must remain attached. When mowing is carried out too early, it may only delay flowering. However, when plants are cut too late in the flowering process, viable seed may still develop in the capitula. As there can be wide variation in plant maturity, a single mowing is unlikely to provide satisfactory control (Sindel, 1991) whereas repeated mowing throughout the entire growing season was successful (Wheatley, 1981). In addition, reduced vegetative matter from mowing will allow autumn herbicide use to be more effective. Besides encouraging competing vegetation where possible, every effort should be made to prevent established plants from going to seed. It is worth mentioning that this kind of control is very labour-intensive.

Chemical Control

Most herbicides give only temporary control of thistles. Young and Evans (1969) reported that application of the expensive and extremely phytotoxic herbicide picloram was the only chemical control method that consistently suppressed O. acanthium in northern California, USA. In Tasmania, Hyde-Wyatt (1968) recommended 2,4-D for overall spraying and, amitrole for spot treatment. In New Zealand, seedlings of O. acanthium were susceptible to emulsifiable esters of 2,4-D, and as young plants, to amitrole, dicamba and picloram (Matthews, 1975). Amitrole and dicamba gave a slow kill of O. acanthium, whereas diquat gave a rapid kill. However, the first two caused unrecoverable damage to adjacent pasture plants, while after application of diquat, pasture plants recovered quickly and even occupied the open spaces left by the killed thistles (Hyde-Wyatt, 1968). At the rosette stage, amitrole, dicamba and diquat have been shown to give effective chemical control of O. acanthium (Hyde-Wyatt, 1968). To control small rosettes, application of dicamba has been recommended (Wheatley, 1981); dicamba + 2,4-D and metsulfuron are also effective (Beck, 1991). Michael (1968) showed that the combined effects of amitrole and competition from five perennial grasses decreased the yield of O. acanthium for the first year of application, but these effects disappeared in two or three years. Application rates can vary, depending on stand density and environmental conditions. Herbicides should generally be applied to rosettes in autumn or in the spring before the plants bolt (Beck, 1991).

Biological Control

Biocontrol agents have been used to control O. acanthium in Australia (Delfosse, 1990), the first being released in 1987. Several potential agents, such as the capitulum weevil Larinus latus, or the stem-boring weevil Lixus cardui, have been released and confirmed as established in the field in 1992 and 1993, respectively. Tephritis postica was introduced into Australia in 1995 (Julien and Griffiths, 1998) and Trichosirocalus briesei in 1997. Studies have been conducted on the biology and impacts of two more potential agents, the rosette-bud weevil Trichosirocalus horridus in Spain (Alonso-Zarazaga and Sanchez-Ruiz, 2002) and the rosette fly Botanophila spinosa in France (Vitou et al., 2001). Surveys in Greece have shown that the weevil L. latus, found only on Onopordum spp., is one of the best candidates for biological control (Davidson, 1990). Scientists are currently evaluating the effectiveness of these control agents on O. acanthium and other Onopordum species (Pettit et al., 1996). No biological control agents are currently available in the USA. Some biocontrol insects released in Australia have failed host specificity tests in the USA and the US Department of Agriculture has been evaluating additional insects for release in the USA (Joley et al., 1998).

Integrated Control

The different control methods that have been used are either not very effective and just temporarily remove a thistle population from the site, or are costly and detrimental to crops (Michael, 1968; Young and Evans, 1969; Wheatley, 1981). The methods that are currently applied create many practical problems (Minehan, 1996), however, a combination of these methods may help prevent this species from further invasion. Pulling out the plants by hand, grazing young plants with goats or using herbicide on young plants to prevent cypsela set, and seeding disturbed areas with competitive native perennials could be parts of an integrated control and management programme.


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