This is another badnasty invasive broom species that you’ll see frequently throughout the Bay Area. Scotch broom (Cytisus scoparius) has pretty yellow pea-like flowers and long, narrow leaves that press closely against its multi-sided stems. Though it occasionally has some rounded leaflets as well, the overall lean, linear look to its foliage makes it easy to tell from its French broom cousin that I wrote about a few weeks ago.
In California, French broom is a nastier problem than Scotch broom, but throughout the rest of the country the Scottish Cytisus scoparius is the worst broom around. Even worse, both were deliberately originally introduced as ornamental species!
This plant is so nasty because it is hearty and vigorous, and spreads fast because it produces a LOT of seeds. A single Scotch broom plant can live for up to 7 years, and produce over 150,000 seeds per year. It’s a mind-boggling number! The seeds stay in the ground, ready to sprout, for between 5 and 30 years. These plants grow up to 12 feet tall and smother any native plants that would otherwise have grown where they are. There’s no sharing if you’re a broom species! Scotch broom is a rampant invasive across much of the western and eastern seaboards of North America – from Alaska to Baja and from Maine to Georgia, as well as in other countries like Australia and New Zealand. It’s native to northern Africa and parts of Europe.
There is one more broom species that you might see in the area, and that’s Portuguese broom. It’s not nearly as common, but it does cover about 65 acres in the Marin Headlands where it was planted in the 1960s as part of a landscaping and slope stabilization program – another good idea gone wrong! Portuguese broom looks a lot like Scotch broom, except the seed pods are inflated instead of compressed around the seeds. Also they have 8-10 sided twigs, as opposed to the 5-sided twigs of Scotch broom.