Common gorse (Ulex europaea) is a prickly evergreen shrub less than ten feet tall, with a profusion of yellow pea-like flowers from March to May. By May plants are covered with half-inch- to one-inch-long brown pods. The short, stout branches are densely packed and may appear leafless. Spines, approximately half an inch long, are located at base of leaves. The somewhat similar species, Scotch broom (Cytisus scoparius), is not prickly.
orse may be slow in spreading and becoming established, but where it gains a hold, there are few other plants that will so completely dominate an area. Besides becoming a significant fire hazard, it can successfully outcompete native plants in part because of its association with nitrogen-fixing bacteria, which facilitate its colonization of nitrogen-poor soils. Gorse leaf litter acidifies and lowers the cation exchange capacity of moderately fertile soils by immobilizing the bases, making it more difficult for native species to establish. On San Bruno Mountain, San Mateo County, gorse is considered the most difficult exotic species to control, and it has caused considerable loss of valuable grassland habitat.