Europe
Scotch broom is a shrub typically growing 3–10 ft (1–3 m) from a forked taproot. Stems are green, star-shaped in cross section, and hairy when young, but less hairy as the plant ages. Leaves are alternate, divided into three segments, and are deciduous. Flowers are usually yellow, up to 1 in (2½ cm) long, and are characteristic of the pea family by being two-parted with an upper and lower lip. Seed pods can grow up to 3 in (7½ cm) long; they are flattened and have hair on the margins, turning brown at maturity. This plant reproduces only by seed.
Scotch broom competes aggressively with other plants for nutrients, light, and water. It displaces native and/or more desirable species, reducing range, pasture, and commercial forest production. Older growth is unpalatable to grazing animals, and toxic compounds in seeds have resulted in livestock death. Although goats, sheep, and wildlife will browse young growth and flowers, the negative impacts outweigh the positive because dense stands of Scotch broom form impenetrable thickets that block access to water and more desirable forage. The high oil content of Scotch broom foliage and seeds and the large amount of dead growth beneath their canopies make Scotch broom an extreme fire hazard.
Andreas, J.E., M.J. Pitcairn, and P.D. Pratt. 2022. Scotch Broom (Cytisus scoparius): History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2022-7-SCOTCH BROOM-P. https://bugwoodcloud.org/resource/files/25361.pdf