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Taurian thistle (Onopordum tauricum)
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ODA rating: A and T
 
USDA Symbol: ONTA
Oregon Taurian thistle distribution

Other common names
bull cottonthistle
 
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Images courtesy of Bob Barrett, Oregon Dept. of Agriculture

If images are downloaded and used from the ODA web site please be sure to credit the photographer.
 
Description
Taurian thistle is a vigorous biennial, or short-lived perennial with coarse, spiny leaves and conspicuous spiny-winged stems. Taurian thistle plants are a nearly florescent lime-green in color with large, mostly singular flower heads at the terminals of the main and side stems. The bright purple flower heads are 3 to 4 inches in diameter. The heads consist of numerous spiny-tipped bracts resembling an artichoke before the bud opens. The leaves are typically covered with short, sticky-glandular hairs, 10-25 cm. long, acutely triangular, with 6 to 8 pairs of spiny-toothed lobes. Taurian thistle seedlings typically appear after the first fall rains and develop into large rosettes the next growing season. From this rosette and taproot an 8 foot tall plant develops. Dead stems can persist into the next season with spines attached. Taurian thistle reproduces only by seed. Most seeds germinate in the fall but can germinate through out the summer. Buried seed can remain viable in the soil seed bank for at least 7 years and possibly to 20 years or more. Wind, water, animals, and vehicles can disperse seeds.
 
Impacts
Due to its growth habits and appearance, it is considered a sister plant to Scotch thistle Onopordum acanthium. Rangeland and openings in ponderosa pine forests are the commonly invaded habitats. Competition from this plant can reduce forage availability and quality especially in drought years. Riparian areas are especially susceptible. Dense stands can form crowding out native vegetation, making some riparian areas and pasture impenetrable for medium to large animals. Studies in Australia have concluded that Taurian thistle has reduced the economic return of infested land by at least 5%. The tall plants can also be a contaminant in alfalfa and grass hay and a troublesome sight-distance for automobiles on right-of-ways. Taurian thistle does not normally form a closed canopy but when it forms dense thickets, grasses and other desirable species are displaced. Often after occupying a site for a few years even Taurian thistle cannot germinate again for some time, leaving bare ground for several years. California has reported several infestations of Taurian thistle from Modoc and Siskiyou counties and has classified it as an "A" rated noxious weed. These counties are just south of Klamath County, Oregon.
 
Introduction
Taurian thistle is native to the Middle East. From Greece, it has spread across Europe into France where there is concern that it is hybridizing with illyrian thistle Onopordum illyricum, another sister plant similar to Scotch thistle. Taurian thistle has only been reported in California and in Colorado. In California, it has infested areas in the Modoc Plateau (Siskiyou County), northern coastal ranges (Monterey County), and the Sierra Nevada foothills, (Yuba County, Nevada County, and Madera County). Colorado has reported Taurian thistle in 2 counties in the Pueblo Mountains but there appears to be confusion as to whether it is actually Taurian or Scotch thistle being reported.
 
Distribution in Oregon
Taurian thistle, Onopordum tauricum was first found in Oregon in 2007, near Klamath Falls. It is the only known site in the state.

 
Biological controls
Biological control agents are not used on "A" listed weeds in Oregon. This weed is being managed for eradication.
 
Informational links
Printable taurian thistle trifold brochure (pdf)