[Knapweeds of the Columbia River Gorge]

St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle

Centaurea solstitialis

Flower head of St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle: Centaurea solstitialis

The photo above shows the flower head of yellow star thistle as seen along Washington Highway 14 at the junction with US 97 in the eastern Columbia River Gorge..........................August 6, 2006.

Characteristics:

Yellow star thistle is really not a thistle, but instead is a species of knapweed. It is a weedy annual or biennial, ranging from 20-80 cm in height. The stems are thinly covered with woolly hairs and appear winged as a result of decurrent leaf bases. The basal leaves, especially those of young seedlings, are deeply lobed or pinnatifid, and may look like those of the common dandelion and range to 20 cm long and 5 cm wide. The stem leaves are reduced in size upwards, becoming linear and entire margined.

The flower heads are few to numerous, located at the ends of the branched stems, with the involucre 10-15 mm tall, and the middle and outer bracts tipped with long spines from 11-22 mm long (note photos). The spines are a straw color. The flowers are yellow.


Habitat:

Yellow star thistle is a bothersome weed of fields, waste areas, and roadsides.


Range:

Native to the Mediterranean region, yellowstar thistle is found over much of the western United States on the east side of the Cascades from Washington to California. It is also becoming established in the upper Rogue Valley of southwestern Oregon.

In the Columbia River Gorge, it is found intermittently east of Bingen, WA between the elevations of 100-600 ft.


Developing flower head (prior to bloom) of St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle: Centaurea solstitialis - St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle: Centaurea solstitialis - Winged stem and stem leaves of St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle: Centaurea solstitialis

Additional close-up views of yellow star thistle as seen at Catherine Creek, Columbia River Gorge.................June 26, 2010.

Stem leaf of St. Barnaby's Thistle, Yellow Star Thistle, Yellow Star-thistle: Centaurea solstitialis

The photo above shows a stem leaf of yellow star thistle as seen along Washington Highway 14 at the junction with US 97 in the eastern Columbia River Gorge..........................August 6, 2006.

Paul Slichter