Taurian thistle (Onopordum tauricum)
Images courtesy Bob Barrett
EDRR Species?:
No
Other common names
Bull cottonthistle
Description
A vigorous biennial or short-lived perennial with coarse, spiny leaves and conspicuous spiny-winged stems. 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 to 25 cm long, acutely triangular, with 6 to 8 pairs of spiny-toothed lobes. 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 throughout the summer. Buried seed can remain viable in the soil seed bank for at least 7 years and possibly 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. 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 percent. The tall plants can also be a contaminant in alfalfa and grass hay and a troublesome sight-distance problem 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 an "A"-rated noxious weed. These counties are just south of Klamath County, Oregon.
