Yellow Starthistle

Centaurea solstitialis L.

Yellow starthistle is a grayish green annual plant that grows 1 to 3 feet tall. The stems of this plant are covered with a white to gray colored, loose, cottony wool. Flowers are a bright yellow color. Flower heads contain long sharp spines about ¾ to 1 inch in length. Yellow starthistle can cause ‘chewing disease’, a nervous disorder, in horses that graze on this plant.