Weeds - Wheat

Contributors to this page: CIMMYT, Mexico (Etienne Duveiller, Monica Mezzalama, Eloise Phipps, Thomas Payne, Jesper Norgaard), Independent consultant (Jesse Dubin).

Creeping thistle, Canada thistle

Creeping thistle, Canada thistle (photo: ICARDA)

Scientific name

Cirsium arvense (L.) Scop.



C. arvense is a noxious weed of the Asteraceae family. It is difficult to eradicate, and is usually introduced accidentally as a contaminant in cereal crop seeds. It is present in Mexico but limited to certain areas. Many countries regulate this plant, or its parts (i.e., seed) as a contaminant.


C. arvense is a serious invasive species in regions where it has been introduced. It is difficult to eradicate because it produces rhizomes.


Cereals and other crops.

Geographic distribution

Native to Europe. Present in the USA, Canada, Mexico, Brazil, South Asia, Brazil, Australia and New Zealand.


C. arvense is a tall, herbaceous, perennial plant, forming extensive clonal colonies from an underground root system that sends up numerous erect stems each spring, reaching 1-1.2 m tall (occasionally more). The stems often lie partly flat by summer but can stay erect if supported by other vegetation. The leaves are very spiny, lobed, up to 15-20 cm long and 2-3 cm wide (smaller on the upper part of the flower stem). The inflorescence is 10-22 mm in diameter, pink-purple in color, with all the florets of similar form (i.e., with no division into disc and ray florets). The flowers are usually dioecious, but not invariably so, with some plants bearing hermaphrodite flowers. The seeds are 4-5 mm long, with a feathery pappus that assists in wind dispersal.

Most seeds germinate within a year, but buried seed can stay dormant for up to 20 years.

Detection/indexing methods used


Procedures followed at the centers in case of positive test

References and further reading

Alberta Invasive Plants Council. Invasive alien species factsheet: Canada thistle (Cirsium arvense). [online] Available from URL: Date accessed 07 April 2010

Blamey M, Grey-Wilson C. 1989. The Illustrated Flora of Britain and Northern Europe. London: Hodder and Stoughton.

United States Department of Agriculture (USDA). PLANTS profile: Cirsium arvense (L.) Scop., Canada thistle. [online] Available from URL: Date accessed 07 April 2010

The Genebanks

The 11 CGIAR genebanks currently conserve 730,000 of cereals and grain legumes, forage crops, tree species, root and tuber crops, bananas and crop wild relatives.