Centaurea solstitialis 

Family: Asteraceae (Sunflower)

Habitat: disturbed areas and grassland

Notes: Invasive non-native. Yellow Starthistle is one of the worst weeds in California. Its deep taproot allows it to out-compete other species for summer soil moisture. Seeds can remain viable for at least three years. While some areas are using Transline (clopyralid) to reduce infestations, this herbicide impacts native species especially in the Sunflower, Carrot and Pea families.