Why Is It a Noxious Weed?
Similar to yellow starthistle, this is an aggressive Centaurea, which is a major problem on annual rangelands in the San Francisco Bay area.
How would I identify it?
Upright branched annual, biennial or short-lived perennial plant growing up to 3.3 feet tall. It is covered with cobwebby hairs often becoming smooth with maturity.
Narrow flowerheads of lavender to deep purple flowers. Spine-tipped bracts subtend the flowerhead with some spines longer at 0.4 to 1.2 inches (1cm to 3cm).
Lower leaves deeply divided, upper leaves are narrow and undivided.
Purple starthistle stems are branched and angled, not winged.
Fruit Seed Description
Purple starthistle seed is small (0.10 to 0.13 inches), white or brown streaked in color and hairless.
Where does it grow?
It can grow in fields, roadsides, disturbed areas, grasslands and overgrazed rangelands. Please click here to see a county level distribution map of purple starthistle in Washington.
How Does it Reproduce?
Purple starthistle reproduces by seed.
How Do I Control It?
Grubbing or digging can be effective for small infestations. Mowing is not effective.
No biological control program is currently being developed for purple starthistle.
For More Information
See our postcard for early detection information about purple starthistle.
See our Written Findings for more information about purple starthistle (Centaurea calcitrapa).