Fuller's Teasel

From California Invasive Plant Council: Dipsacus sativus (fullers teasel) is a biennial (family Dipsacaceae) found in California’s Coastal and Peninsular Ranges and the San Francisco Bay area. It favors disturbed sites, including grasslands, roadsides, ditches and riparian sites. Fullers teasel’s spiny flower heads were used for carding wool before metal carding combs were created. Teasel plants may grow to form dense stands that are impenetrable by humans and animals. Teasel seeds can survive in the soil for 6 years or more, and once a dense population is established, it can persist for decades. Small populations may be mechanically controlled by removing plants to a few inches below the root crown.