This native of Eurasia is a long-lived, taprooted perennial that grows 1 1/2 to 3 feet (50 to 90 cm) tall.
The stems of the Squarrose knapweed are very branched, with deeply dissected lower leaves and bract-like upper leaves arranged alternately along their length.
Flower clusters are small with 4 to 8 rose or pink colored flowers each. The flowers are small too, less than 1/2 inch (10 mm) long with an urn shaped base covered with bracts, usually developing no more than 3 to 4 seeds per head. The bract tips are recurved or spreading and have terminal spines longer than the lateral spines on each bract.
Each flower produces 3 to 4, 1/8 inch (3 mm) long, dull brown seeds with straw-colored lines and bristles about half as long as the seed.
Squarrose knapweed is a competitive weed native to the eastern Mediterranean area. It is not common, but it is an invasive weed found in surrounding states of Nevada, Oregon and Utah. Seeds are easily spread by livestock and wildlife.
Squarrose knapweed is often confused with diffuse knapweed, but differs in that it is a true perennial and the flower heads have recurved bract tips and unlike the diffuse knapweed, the seed heads fall off the stems soon after the seeds mature.