Turkish thistle
Carduus cinereus
Washington State Classification
Class A — Eradication Required Statewide
Turkish thistle is documented as spreading on its own in Oregon and Idaho, competing with and crowding out native vegetation and desirable forage plants.
Quick Reference
Identification
Growth Habit
Turkish thistle is an annual thistle with winged stems that can grow up to 4 feet tall. Its basal leaves are up to 4 inches long, and stem leaves reduce in size moving up the stem. Flower heads are compressed, non-spherical, and single or in loose clusters. Each purplish flower head is typically on a short hairy stem or may be stemless.
Leaves
Turkish thistle plants have basal leaves and stem leaves. The basal leaves taper to winged petioles and are up to 4 inches long and have lobed edges (2 to 5 lobes). The undersides of the leaves are tomentose (with woolly hairs) while the upper surfaces are loosely woolly. The stem leaves attach directly to the stem and reduce in size going up the stems toward the tips.
Flowers
The flower heads are non-spherical, somewhat compressed, and narrow towards the purplish flowers. They occur singly or in loose groups of 2 to 5. A key identifying trait is that the flower heads are often on short stems (pedunculate). These flower head stems are 0 to 1.2 inches (0 to 3 cm) long and are covered in woolly hairs.
Fruit & Seeds
Each seed is golden brown to brown in color, 0.16 to 0.24 inches long, and has a bristly tuft (pappus) at one end.
Impact
Turkish thistle is documented as spreading on its own in Oregon and Idaho, competing with and crowding out native vegetation and desirable forage plants. It has been noted to spread readily and be competitive in native rangelands in NE Oregon. Other Carduus species are known to be weedy and invade rangelands, meadows, pastures, and fields in Washington and the Pacific Northwest. So far, Turkish thistle is not known to occur in Washington but it is spreading close by in Oregon and Idaho and could readily invade here.
Ecology & Spread
Habitat
Turkish thistle plants have been found in Oregon and Idaho, growing on canyon grasslands, which include scattered shrubs and trees, and are often dominated by native bunchgrasses. Turkish thistle grows on dry rocky talus slopes on southern aspects as well as sites with deeper soils in more mesic sites. Plants also grow along ephemeral streams, following their edges downhill. Click hereto see a county-level distribution of Turkish thistle in Washington.
Spread Mechanisms
Reproduction
Turkish thistle reproduces by seed, it is not known to spread vegetatively.
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