One of the most common thistles around is bull thistle, an invasive species from Europe. Its showy purple flowers are beloved by bumble bees and other insects, but its spiny leaves are a bane to ranchers.
Bull thistle (Cirsium vulgare) grows most abundantly in coastal grasslands, along the edge of marshes, and in sunny openings in forests, according to the California Invasive Plant Council – but it is found in every state in the country. You can recognize this species because the leaves don’t stop when they meet the stem; instead they run down along it like little spiny wings.
This plant thrives on disturbance; it grows most readily when the soil is disrupted by plowing, logging, digging and so on. Even gopher activity can give it a boost!
Flowers Of Marin 