Published March 1989. A more recent revision exists. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalog
These thistles are native to Europe and the Middle East.
Some are not true thistles; for example, purple/Iberian and
yellow starthistle actually are knapweeds. All of these plants, however,
share a spiny, thorny, invasive nature and long-lasting, hard seed. These traits make people who use or manage land for recreation,...
Despite its common name, Canada thistle is not native
to Canada; rather, it is from the temperate regions
of Eurasia. It is an aggressive, creeping perennial
that reproduces from seed and from vegetative buds in its
root system. It is difficult to control because its
root system is extensive. Horizontal...