Taxonomy

This annual plant grows between 60 and 90 cm (2 to 3 feet) tall and has stiff branching stems that are covered with white hairs.

The flowers are bright yellow and a single one grows on the end of each branch.  Beneath the flower head are long (10-25 mm) straw-colored spines that form a star pattern.

Yellow starthistle is separated from closely related species by a combination of flower corolla length and spine length.