With flamboyant, showy flowers, Spanish broom is probably the most beautiful of all the evil brooms. It is still evil, though. Don’t be fooled by the big yellow flowers with their many exuberant stamens and pretty wing-like petals.
This plant has the lean, linear look of Scotch broom but with even fewer leaves. The California Invasive Plant Council lists Spanish broom (Spartium junceum) as a species that can cause serious problems for native ecosystems. It can grow up to 15 feet tall and form dense stands that smother all other plants in the area. According the IPC, it is native to Spain, Morocco and other parts of southern Europe. It was introduced to California in 1848 as a decorative plant, and in the 1930s was planted along mountain highways in Southern California. Oops.
In Marin, it is one of the least common brooms. I saw the ones pictured here clinging to the slopes of what looks like an old rock quarry owned by the Marin Municipal Water District.