Sometimes, you are distracted by a huge display of colour; the startlingly patterned fur of a Bengal Tiger (Panthera tigris tigris) can distract for a second – and that is enough to get you eaten. The example of Scotch Broom (Cytissus scoparius) you see here – in my cousin’s garden at Matlock, Derbyshire - is a riot of colour, a profusion of yellow and red flowers held closely to spiky green stems. There are many Brooms; the Common, Spanish, Provence and Atlas Broom are all cultivated horticultural plants, and like another member of the Fabaceae, the Common Gorse (Ulex europaeus), they are truly prolific. Their ripe seed pods twist open with a sharp snapping sound, which throws their legume-like seeds a fair distance from the parent plant. It makes a brave show on the rocky Derbyshire soil and causes you to forget that, in other places, this decorative member of the Fabaceae, or pea family, can be a source of great problems. Just like the Common Gorse, they fix nitrogen via bacteria (Rhizobium legumionsarum is the classic species) which are contained in nodules on their root system, thereby fertilizing their own growth. Consequently, they can thrive where other plants cannot. This explains why Scotch Broom was imported to parts of North America, not just as decorative shrubs, but as plants which could be utilized to reclaim areas suffering from soil erosion; it was particularly used to help stabilize recently excavated earth alongside new roadways. Since the seeds can lie dormant for up to 80 years before germinating, it can be said to be one of the major invasive plant species. It has spread from Maine down to Georgia, and as far west as Wisconsin. On the Pacific coast Scotch Broom is now everywhere from Alaska to California; in Canada (following its introduction on Vancouver Island in 1850) it is now found in Nova Scotia and British Columbia.
In Washington State, Scotch Broom classified as a Class B Noxious Weed, and parts of King County have problems with large stands of the plant which displaces local flora, and offers few chances for habitat exploitation by native animals and birds due to the fact that the seeds (and other parts of the plant) are toxic. Because of the dense stands of plants they form, they are affecting the grassland habitat of the Roosevelt Elk (Cervus canadensis roosevelti), the largest of the four North American elk species, and one which inhabits the Pacific Northwest. A relative of the Broom is Dyer’s Greenweed (Genesta tinctoria), which is found in New England; as its Latin name suggests, it was used (along with the blue from woad) to produce a useful green due, favoured until the 18th century.
New Zealand is the site of major infestations, and economic losses in agriculture and the forestry industry are significant. Scotch Broom is also found in Chile, Australia, Iran, South Africa and India. In recent years, biological control has been attempted, with the following species being investigated – Scotch Broom Bruchid (Bruchidius villosus), Broom Psyllid (Arytainilla spartiophylla), Broom Twig Miner (Leucoptera spartifoliella), Broom Gall Mite (Aceria genistae), Broom Leaf Beetle (Gonicotena olivacea), and the Broom Shoot Moth (Agonopterix assimilella). With this array of potential controls there is some hope for reduction, if not eradication.
Strangely, the Common Broom (then known as Planta genista) gave its name to a European Royal house in the 12th century. Geoffrey V of Anjou (an area of northern France) selected the flower as his personal badge due to its golden colour. His descendants included Henry II, King of England (1133 – 1189), who founded the Plantagenet dynasty.
The Scots Broom may look beautiful at times, but its economic costs would seem to outweigh its attractiveness.