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
Don't need the entire report?
Generate a print friendly version containing only the sections you need.Generate report
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 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 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 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).
DescriptionTop 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 TypeTop of page Annual
DistributionTop 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 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.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|-Xinjiang||Present||Native||Flora of China Editorial Committee, 2003|
|Georgia (Republic of)||Present||Native||USDA-ARS, 2003|
|India||Present, few occurrences||Parsons and Cuthbertson, 2000|
|-Jammu and Kashmir||Present||Native||Polunin and Stainton, 1984|
|Jordan||Present||Native||Abuharfeil et al., 2001|
|Turkey||Present||Native||Danin, 1975; Holm et al., 1979|
|Uzbekistan||Present||Native||Gigieniva and Umarov, 1981|
|Canada||Present||Introduced||before 1867||Invasive||Hubbert, 1867; Darbyshire, 2003|
|-British Columbia||Present||Introduced||Invasive||Darbyshire, 2003|
|-New Brunswick||Present||Introduced||Darbyshire, 2003|
|-Newfoundland and Labrador||Present||Introduced||Darbyshire, 2003|
|-Nova Scotia||Present||Introduced||Darbyshire, 2003|
|USA||Present||Introduced||late 1800||Invasive||Bentham and Hooker, 1904; Holm et al., 1979|
|-California||Present||Introduced||Invasive||Young and Evans, 1969; Keil and Turner, 1993|
|-Colorado||Present||Introduced||Invasive||Weber and Wittmann, 1996|
|-Connecticut||Present||Introduced||Mehrhoff et al., 2003|
|-Idaho||Present||Introduced||Invasive||Callihan and Miller, 1994; USDA-NRCS, 2002|
|-Illinois||Restricted distribution||Introduced||Jones and Fuller, 1955; USDA-NRCS, 2002|
|-Indiana||Restricted distribution||Introduced||Deam, 1940|
|-Iowa||Present, few occurrences||Introduced||Not invasive||Cratty, 1932; USDA-NRCS, 2002|
|-Kansas||Present||Introduced||Great Plain Flora Association, 1986|
|-Michigan||Present||Introduced||Deam, 1940; Britton and Brown, 1970|
|-Nebraska||Restricted distribution||Introduced||Nebraska Department of Agriculture, 1979; McCarty et al., 1984|
|-Nevada||Present||Introduced||Invasive||Young and Evans, 1969|
|-New Jersey||Present||Introduced||Britton and Brown, 1970; USDA-NRCS, 2002|
|-New Mexico||Present||Introduced||Invasive||Sivinski et al., 1994; USDA-NRCS, 2002|
|-New York||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-Ohio||Present, few occurrences||Introduced||Fisher, 1988; USDA-NRCS, 2002|
|-Oklahoma||Present||Introduced||Great Plain Flora Association, 1986|
|-Oregon||Present||Introduced||Invasive||Peck, 1961; French et al., 1999|
|-Pennsylvania||Present||Introduced||Britton and Brown, 1970; USDA-NRCS, 2002|
|-Rhode Island||Present||Introduced||USDA-NRCS, 2002|
|-South Carolina||Present||Introduced||Batson, 1975|
|-South Dakota||Present||Introduced||USDA-NRCS, 2002|
|-Texas||Present||Introduced||Correll and Johnston, 1970; USDA-NRCS, 2002|
|-Utah||Present||Introduced||Holmgren and Andersen, 1970; USDA-NRCS, 2002|
|-Washington||Present||Introduced||Invasive||Gaines and Swan, 1972|
|-West Virginia||Present||Introduced||USDA-NRCS, 2002|
|Argentina||Present||Introduced||Invasive||Cabrera, 1971; Boeleke, 1986|
|Chile||Present||Introduced||Matthei and Marticorena, 1990|
|Albania||Present||Native||Tutin et al., 1976|
|Austria||Present||Native||Tutin et al., 1976; Raabe, 1988|
|Belgium||Present||Native||Tutin et al., 1976|
|Bulgaria||Present||Native||Tutin et al., 1976|
|Croatia||Present||Native||Williams and Hunyadi, 1987|
|Czech Republic||Present||Native||Tutin et al., 1976|
|Finland||Present||Native||Moore and Frankton, 1974|
|France||Present||Native||Tutin et al., 1976; Guinochet and Vilmorin, 1982|
|-Corsica||Present||Native||Tutin et al., 1976|
|Germany||Present||Native||Tutin et al., 1976|
|Greece||Present||Native||Tutin et al., 1976|
|Hungary||Present||Native||Tutin et al., 1976|
|Italy||Present||Native||Tutin et al., 1976|
|Netherlands||Present||Native||Tutin et al., 1976|
|Poland||Present||Native||Szafer, 1966; Holm et al., 1979|
|Portugal||Present||Native||Tutin et al., 1976|
|Romania||Present||Native||Tutin et al., 1976|
|Russian Federation||Present||Native||Czerepanov, 1995|
|-Central Russia||Present||Native||Tutin et al., 1976|
|-Eastern Siberia||Present||Native||USDA-ARS, 2003|
|-Russian Far East||Present||Native||Zarubin et al., 1993|
|-Southern Russia||Present||Native||Tutin et al., 1976|
|-Western Siberia||Present||Native||USDA-ARS, 2003|
|Serbia||Present||Native||Williams and Hunyadi, 1987|
|Slovakia||Present||Native||Williams and Hunyadi, 1987|
|Spain||Present||Native||Tutin et al., 1976; Caballero, 1984|
|Sweden||Present||Native||Tutin et al., 1976|
|Switzerland||Present||Native||Tutin et al., 1976|
|UK||Present||Native||Tutin et al., 1976; Holm et al., 1979|
|Yugoslavia (former)||Present||Native||Tutin et al., 1976|
|Australia||Present||Introduced||Invasive||Willis, 1972; Holm et al., 1979|
|-New South Wales||Present||Introduced||Invasive||Groves et al., 1990|
|-South Australia||Present||Introduced||Auld and Medd, 1987|
|-Tasmania||Present||Introduced||Invasive||Curtis, 1963; Hyde-Wyatt and Morris, 1980|
|-Victoria||Present||Introduced||before 1850||Invasive||Willis, 1972|
|-Western Australia||Present||Introduced||Grieve and Blackall, 1975|
|New Zealand||Present||Introduced||1880||Holm et al., 1979; Webb et al., 1988|
History of Introduction and SpreadTop 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 IntroductionTop 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.
HabitatTop 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 ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||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)|
|Terrestrial ‑ Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Riverbanks||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop 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 AffectedTop of page
Growth StagesTop of page Pre-emergence, Seedling stage, Vegetative growing stage
Biology and EcologyTop 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).
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 Uniform
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 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 DispersalTop 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).
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 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 ImpactTop 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: BiodiversityTop 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 ImpactTop 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 FactorsTop 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
- 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 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/ConditionsTop 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 ControlTop 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).
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.
ReferencesTop of page
Abuharfeil NM; Maher S; Kleist S von; von Kleist S, 2001. Augmentation of natural killer cell activity in vivo against tumor cells by some wild plants from Jordan. Phytotherapy Research, 15:109-113.
Alex JF, 1992. Ontario weeds. Publ. No. 505. Toronto, Canada: Queen's Printer for Ontario.
Alonso-Zarazaga MA; Sanchez-Ruiz M, 2002. Revision of the Trichosirocalus horridus (Panzer) species complex, with description of two new species infesting thistles (Coleoptera: Curculionidae, Ceutorhynchinae). Australian Journal of Entomology, 41(3):199-208; 26 ref.
Auld BA; Medd RW, 1987. Weeds - An Illustrated Botanical Guide to the Weeds of Australia. Melbourne, Australia: Inkata press.
Batson WT, 1975. Genera of the Eastern Plants, edition 2. Columbia, South Carolina, USA: The State Printing Co.
Beck KG, 1991. Biennial thistle control with herbicides. In: James LF, Evans JO, Ralphs MH, Child RD, eds. Noxious range weeds. Boulder, Colorado, USA: Westview Press, 254-259.
Beck KG, 1999. Biennial thistles. In: Sheley RL, Petroff JK, eds. Biology and Management of Noxious Rangeland Weeds. Corvallis, Oregon, USA: Oregon State University Press, 145-161.
Bentham G; Hooker JD, 1904. Handbook of the British flora. London, UK: L. Reeve and Co.
Boeleke O, 1986. Plantas vasculares de la Argentina: nativas y exóticas. Buenos Aires, Argentina: Editorial Hemisferio Sur SA.
Boissier E, 1875. Flora Orientalis, Vol. 3. Geneva & Basle, Switzerland: H. Georg.
Bremness L, 1989. The Complete Book of Herbs. Montreal, Canada: The Reader's Digest Association (Canada) Ltd.
Briese DT; Thomann T; Vitou J, 2002. Impact of the rosette crown weevil Trichosirocalus briesei on the growth and reproduction of Onopordum thistles. Journal of Applied Ecology, 39(4):688-698; 22 ref.
Britton NL; Brown A, 1970. An illustrated flora of the northern United States and Canada, Vol. III, edition. New York, USA: Dover Publications, Inc.
Caballero A, 1984. Floras of the world, Vol. 3. Flora Analítica de Espana. Koenigstein, West Germany: Koeltz Scientific Books.
Cabrera AL, 1971. Compositae. In: Correa MN, ed. Flora Patagonica. Part VII. Buenos Aires, Argentina: Coleccion Cientifica del INTA, Instituto Nacional de Tecnologia Agropecuaria, 283- 285.
Callihan RH; Miller TW, 1994. A Pictorial Guide to Idaho's Noxious Weeds. Boise, Idaho, USA: Idaho Department of Agriculture.
Correll DS; Johnston MC, 1970. Manual of the vascular plants of Texas. Renner, Texas, USA: Texas Research Foundation.
Cratty RI, 1932. The Iowa Flora. Iowa, USA: Iowa State College.
Cristofaro M; Lecce F; Paolini A; Cristina Fdi; Gültekin L; Smith L, 2013. Field explorations in anatolia for the selection of specific biological control agents for Onopordum acanthium (Asteraceae). In: Proceedings of the XIII International Symposium on Biological Control of Weeds, Waikoloa, Hawaii, USA, 11-16 September, 2011 [ed. by Wu, Y.\Johnson, T.\Sing, S.\Raghu, S.\Wheeler, G.\Pratt, P.\Warner, K.\Center, T.\Goolsby, J.\Reardon, R.]. Hilo, USA: USDA Forest Service, Pacific Southwest Research Station, Institute of Pacific Islands Forestry, 186.
Curtis WM, 1963. The Student's Flora of Tasmania, Part 2. Tasmania: LG Shea, Government Printer.
Czerepanov SK, 1995. Vascular Plants of Russia and Adjacent States (The Former USSR). Cambridge, UK: Cambridge University Press.
Danin A, 1975. Onopordum. In: Davis PH, ed. Flora of Turkey and the east Aegean Islands, Vol. 5. Edinburgh, UK: University Press, 356-369.
Darbyshire SJ, 2003. Inventory of Canadian agricultural weeds. Ottawa, Canada: Agriculture and Agri-Food Canada.
Deam CC, 1940. Flora of Indiana. Indianapolis, Indiana, USA: Wm. B. Burford Printing Co.
Dewey SA, 1991. Weed thistles of the western United States. In: James LF, Evans JO, Ralphs MH, Child RD, eds. Noxious Range Weeds. Boulder, Colorado, USA: Westview Press, 247-253.
Fisher TR, 1988. The Dicotyledoneae of Ohio. Columbus, Ohio, USA: Ohio State University Press.
Flora of China Editorial Committee, 2003. Flora of China Web. Cambridge, Massachusetts, USA: Harvard University Herbaria. http://flora.huh.harvard.edu/china/.
French K; Burrill LC; Butler TV, 1999. Problem Thistles of Oregon. Corvallis, Oregon, USA: Oregon State University.
Gaines XM; Swan DG, 1972. Weeds of Eastern Washington and Adjacent Areas. Davenport, Washington, USA: Camp-Na-Bor-Lee Association, Inc.
Georgieva J; Lakova M; Spirkov D, 1973. Further study of the form obtained after crossing Helianthus annuus L. with Onopordum acanthium L. Genet Sel, 4:397-408.
Gigieniva EI; Umarov AU, 1981. Nonglycerids seed cover lipids of Artemisia absinthium and Onopordum acanthium. Khimiya Prirodnykh Soedinenii, 0:154-157.
Glasby JS, 1991. Dictionary of Plants Containing Secondary Metabolites. London, UK: Taylor and Francis Ltd.
Gonzalez-Sierra G; Perez-Morales C; Penas-Merino A; Rivas-Martinez S, 1992. Taxanomical revision of species of Onopordum genus from Spain. Candollea, 47:181-213.
Great Plain Flora Association, 1986. Flora of the Great Plains. Kansas, USA: University Press of Kansas.
Grieve BJ; Blackall WE, 1975. How to Know Western Australian Wildflowers. Nedlands, Western Australia: University of Western Australia Press.
Guinochet M; Vilmorin R, 1982. Flore de France. Fascicule 4. Paris, France: Centre National de la Recherche Scientifique.
Hamilton GH, 1943. Plants of the Niagara Parks System of Ontario. Toronto, Canada: The Ryerson Press.
Harden GH, 1992. Flora of New South Wales, Vol. 3. Kensington, NSW, Australia: New South Wales University Press.
Haughton CS, 1978. Green Immigrants: the Plants that Transformed America. New York, USA: Harcourt Brace Jovanovich, Inc.
Hilston NW, 1969. Weeds of Wyoming. Bulletin 498. Laramie, Wyoming, USA: University of Wyoming, Agricultural Experiment Station.
Holm L; Pancho JV; Herberger JP; Plucknett DL, 1979. A Geographical Atlas of World Weeds. Toronto, Canada: John Wiley and Sons Inc.
Holmgren AH; Andersen BA, 1970. Weeds of Utah. Logan, Utah, USA: Utah State University.
Hooper JF; Young JA; Evans RA, 1970. Economic evaluation of Scotch thistle suppression. Weed Science, 18:583-586.
Hubbert J, 1867. Catalogue of the flowering plants and ferns indigenous to, or naturalized in Canada. Montreal, Canada: Dawson Brothers.
Hyde-Wyatt BH, 1968. Cotton thistle. Tasmania Journal of Agriculture, 39:43-46.
Hyde-Wyatt BH; Morris DI, 1980. The noxious and secondary weeds of Tasmania. Tasmania, Australia: Department of Agriculture.
Jessop JP; Toelken HR; eds, 1986. Flora of South Australia, edition 4. Vol. 3, 1634-1635.
Joley DB; Woods DM; Pitcairn; MJ, 1998. Field studies to examine growth habit and population resurgence of Scotch thistle in northern California. CDFA biological control program: Annual report. California, USA: California Department of Food and Agriculture.
Jones GN; Fuller GD, 1955. Vascular plants of Illinois. Urbana, Illinois, USA: The University of Illinois Press.
Julien MH; Griffiths MW, 1998. Biological control of weeds: a world catalogue of agents and their target weeds. Biological control of weeds: a world catalogue of agents and their target weeds., Ed. 4:x + 223 pp.
Keil DJ; Turner CE, 1993. Onopordum. In: Hickman JC, ed. The Jepson Manual: Higher Plants of California. Berkeley and Los Angeles, USA: University of California Press, 320.
Lehr JH, 1978. A Catalogue of the Flora of Arizona. Phoenix, Arizona, USA: Desert Botanical Garden.
Lindley DC, 2003. Horizon Herbs, LLC. Williams, Oregon, USA. http://www.horizonherbs.com.
Matthei O; Marticorena C, 1990. Weeds of the family Asteraceae new for the flora of Chile. Gayana, Botanica, 47:57-63.
McCarty MK; Scifres CT; Robinson LR, 1984. A descriptive guide for major Nebraska thistles. Publication, Nebraska Agricultural Experiment Station, 493:1-27.
Mehrhoff LJ; Metzler KJ; Corrigan EE, 2003. Non-native and Potentially Invasive Vascular Plants in Connecticut. Storrs, Connecticut, USA: University of Connecticut, Center for Conservation and Biodiversity.
Meier LR, 1995. Variation in seeds of Onopordum acanthium. MSc thesis. University of Western Ontario, London, Canada.
Michael PW, 1968. Control of the biennial thistle, Onopordum, by amitrole and five perennial grasses. Australian Journal of Experimental Agriculture and Animal Husbandry, 8:331-339.
Moore RJ; Frankton C, 1962. Cytotaxonomic studies in the tribe Cynareae (Compositae). Canadian Journal of Botany, 40:281-293.
Mucina L, 1989. Syntaxonomy of the Onopordum acanthium communities in temperate and continental Europe. Vegetatio, 81:107-115.
Nebraska Department of Agriculture, 1979. Nebraska Weeds. Lincoln, Nebraska, USA: Department of Agriculture, Weed Division.
Nevskii VP, 1929. Aphids of Central Asia. Tashkent, Uzbekistan: Uzbekistan Plant Protection Experimental Station, 16:1-425.
Parsons WT; Cuthbertson EG, 2000. Noxious Weeds of Australia, edition 2. Orange, New South Wales, Australia: NSW Agriculture.
Peck ME, 1961. A Manual of the Higher Plants of Oregon, edition 2. Portland, Oregon, USA: Oregon State University Press.
Pérez-García F, 1993. Effect of the origin of cypsela on germination of Onopordum acanthium L. (Asteraceae). Seed Science and Technology, 21:187-195.
Piper G, 1984. Scotch thistle - a continuing menace in the Pacific Northwest. Pacific Northwest Weed Topics, 84:1-2.
Podlech D; Dieterle A, 1969. Chromosomenstudien an Afghanischen Pflanzen. Candollea, 24:185-243.
Qaderi MM, 1998. Intraspecific variation in germination of Scotch thistle (Onopordum acanthium L.) cypselas. MSc thesis. University of Western Ontario, London, Canada.
Qaderi MM, 2002. Pre- and post-dispersal factors affecting cypsela dormancy in Scotch thistle, Onopordum acanthium (Asteraceae). PhD thesis. University of Western Ontario, London, Canada.
Qaderi MM; Cavers PB, 2000. Variation in germination response within Scotch thistle, Onopordum acanthium L., populations matured under greenhouse and field conditions. E^acute~coscience, 7(1):57-65; 57 ref.
Qaderi MM; Cavers PB, 2003. Effects of dry heat on the germinability and viability of Scotch thistle (Onopordum acanthium) cypselas: interpopulation and interposition variation. Canadian Journal of Botany, 81:684-697.
Qaderi MM; Cavers PB; Bernards MA, 2003. Isolation and structural characterization of a water-soluble germination inhibitor from Scotch thistle (Onopordum acanthium) cypselas. Journal of Chemical Ecology, 29:2407-2420.
Qaderi MM; Cavers PB; Bernards MA, 2003. Pre- and post-dispersal factors regulate germination patterns and structural characteristics of Scotch thistle (Onopordum acanthium) cypselas. New Phytologist, 159(1):263-278; many ref.
Radford AE, 1986. Fundamentals of Plant Systematics. New York, USA: Harper and Row, Publishers.
Rechinger KH, 1979. Flora Iranica. Compositae III-Cynareae. Graz, Austria: Akademische Druck- u. Verlagsanstalt.
Scifres CJ; McCarty MK, 1969. Some factors affecting germination and seedling growth of Scotch thistle. Research Bulletin, Nebraska Agricultural Experiment Station, 228:1-29.
Sivinski R; Lowrey R; Peterson R, 1994. Additions to the native and adventive flora of New Mexico. Phytologia, 76:473-479.
Stewart WG; James LE, 1969. A guide to the flora of Elgin County Ontario. St. Thomas, Ontario, Canada: Catfish Creek Conservation Authority.
Steyermark JA, 1963. Flora of Missouri. Ames, Iowa, USA: The Iowa State University Press.
Szafer W, 1966. The Vegetation of Poland. Oxford, UK: Pergamon Press.
Thomas AG, 1976. 1976 Weed survey of cultivated land in Saskatchewan. Regina, Canada: Agriculture Canada, 93 pp.
Toole EH; Brown E, 1946. Final results of the Duval buried seed experiment. Journal of Agricultural Research, 72:201-210.
Tutin TG; Heywood VH; Burges NA; Moore DM; Valentine DH; Walters SM, Webb DA (et al. editors), 1976. Flora Europaea. Volume 4. Plantaginaceae to Compositae (and Rubiaceae). Cambridge, UK: University Press, xxix + 505 + 5pp + 5 maps.
USDA-ARS, 2003. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx
USDA-NRCS, 2002. The PLANTS Database, Version 3.5. National Plant Data Center, Baton Rouge, USA. http://plants.usda.gov.
Vitou J; Briese DT; Sheppard AW; Thomann T, 2001. Comparative biology of two rosette crown-feeding flies of the genus Botanophila (Dipt., Anthomyiidae) with potential for biological control of their thistle hosts. Journal of Applied Entomology, 125(1/2):89-95; 12 ref.
Vorobiov MY, 1960. On certain biological features of biennial weeds of the Danube steppe. Ukrain Botanichnii Zhurnal, 17:43-49.
Watson AK, 1986. Morphological and biological parameters of the knapweed nematode, Subanuguina picridis. Journal of Nematology, 18:154-158.
Webb CJ; Sykes WR; Garnock-Jones PJ, 1988. Flora of New Zealand Volume IV. Naturalised Pteridophytes, Gymnosperms and Dicotyledons. Christchurch, New Zealand: DSIR Botany Division, 1365 pp. http://floraseries.landcareresearch.co.nz/pages/Book.aspx?fileName=Flora%204.xml
Weber WA; Wittmann RC, 1996. Colorado Flora: Eastern Slope, edition 2. Niwot, Colorado, USA: University Press of Colorado.
Williams G, 1982. Elsevier's Dictionary of Weeds of Western Europe. Amsterdam, The Netherlands: Elsevier Scientific Publishing Company.
Williams G; Hunyadi K, 1987. Dictionary of Weeds of Eastern Europe. Amsterdam, Netherlands: Elsevier.
Willis JH, 1972. A handbook to plants in Victoria. Carlton, Victoria, Australia: Melbourne University Press.
Young JA; Evans RA, 1969. Control and ecological studies of Scotch thistle. Weed Science, 17:60-63.
Zarubin AM; Ivanova MM; Lyakhova IG; Baritskaya VA; Ivel'skaya VI, 1993. Floristic finds in the Lake Baikal region. Botanicheskii Zhurnal (St. Petersburg), 78:93-101.
Distribution MapsTop of page
Unsupported Web Browser:
One or more of the features that are needed to show you the maps functionality are not available in the web browser that you are using.
Please consider upgrading your browser to the latest version or installing a new browser.
More information about modern web browsers can be found at http://browsehappy.com/