Onopordum acanthium (scotch thistle)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Rainfall Regime
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Plant Trade
- Impact Summary
- Environmental Impact
- Impact: Biodiversity
- Social Impact
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
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
- ONRAC (Onopordum acanthium)
Summary of InvasivenessTop of page
Taxonomic TreeTop 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 NomenclatureTop of page
DescriptionTop of page
Plant TypeTop of page
DistributionTop of page
Distribution TableTop of page
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.Last updated: 25 Feb 2021
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|China||Present||Present based on regional distribution.|
|India||Present, Few occurrences|
|-Jammu and Kashmir||Present||Native|
|Federal Republic of Yugoslavia||Present||Native|
|-Russian Far East||Present||Native|
|Canada||Present||Introduced||Invasive||First reported: before 1867|
|-Newfoundland and Labrador||Present||Introduced|
|United States||Present||Introduced||Invasive||First reported: late 1800|
|-Iowa||Present, Few occurrences||Introduced|
|-Ohio||Present, Few occurrences||Introduced|
|-New South Wales||Present||Introduced||Invasive|
|-Victoria||Present||Introduced||Invasive||First reported: before 1850|
History of Introduction and SpreadTop of page
Risk of IntroductionTop of page
HabitatTop of page
Habitat ListTop of page
|Terrestrial||Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Urban / peri-urban areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Riverbanks||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page
Biology and EcologyTop of page
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).
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).
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 RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop 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|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Dry season duration||1||2||number of consecutive months with <40 mm rainfall|
|Mean annual rainfall||500||2000||mm; lower/upper limits|
Rainfall RegimeTop of page
Soil TolerancesTop of page
Special soil tolerances
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Botanophila spinosa||Herbivore||Growing point|
|Trichosirocalus briesei||Herbivore||Growing point|
Notes on Natural EnemiesTop of page
Means of Movement and DispersalTop of page
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).
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.
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).
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 VectorsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|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|
|Stems (above ground)/Shoots/Trunks/Branches|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page
Environmental ImpactTop of page
Impact: BiodiversityTop of page
Social ImpactTop of page
Risk and Impact FactorsTop of page
- 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
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Negatively impacts agriculture
- Negatively impacts animal health
- Negatively impacts tourism
- Reduced amenity values
- Reduced native biodiversity
- Competition - monopolizing resources
- Pest and disease transmission
- Produces spines, thorns or burrs
- Highly likely to be transported internationally accidentally
- Highly likely to be transported internationally deliberately
- Difficult/costly to control
UsesTop of page
Similarities to Other Species/ConditionsTop of page
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.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).
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.
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).
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).
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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