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Yellow Starthistle (Centaurea solstitialis)

Yellow starthistle is a member of the Aster or Sunflower family, Thistle tribe, and is an introduced annual which reproduces by seeds. The stem is white-woolly and branches from the base and above to form a bushy plant, 1 to 2 feet tall. The leaves are whitewoolly, and are deeply lobed, two to three inches long. The upper leaves are narrow, pointed, and much smaller. The yellow flowers, located singly on the ends of branches, have outwardly-pointed, stiff, yellow spines up to one inch long. The plant may have two types of seeds: one is light colored with a tuft of soft bristles; the other is dark with no bristles.

Yellow starthistle may grow in many different soil types. It frequents roadsides and neglected areas. The plant, while not yet common in Colorado, is considered a serious rangeland threat in our northern neighboring states (infests approximately 10 million acres in California).

Yellow starthistle in Larimer County and Colorado

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