Cytisus scoparius

Classification

There are two subspecies of Cytisus scoparius:

Description

Plants of Cytisus scoparius typically grow to 1–3 m (3.3–9.8 ft) tall, rarely to 4 m (13 ft), with main stems up to 5 cm (2.0 in)thick, rarely 10 cm (3.9 in). The shrubs have green shoots with small deciduous trifoliate leaves 5–15 mm long, and in spring and summer is covered in profuse golden yellow flowers 20–30 mm from top to bottom and 15–20 mm wide. Flowering occurs after 50–80 growing degree days. In late summer, its legumes (seed pods) mature black, 2–3 cm long, 8 mm broad and 2–3 mm thick; they burst open, often with an audible crack, forcibly throwing seed from the parent plant. This is the hardiest species of broom, tolerating temperatures down to about −25 °C (−13 °F). C. scoparius contains toxic alkaloids that depress the heart and nervous system.

Distribution and habitat

Cytisus scoparius is found in sunny sites, usually on dry, sandy soils at low altitudes. In some places outside of its native range, such as India, South America and western North America, particularly Vancouver Island, it has become an ecologically destructive colonizing invasive species in grassland, shrub and woodland, and other habitats. It is common in Great Britain and Ireland.

As a legume, this shrub can fix nitrogen in the soil through a symbiotic relationship with Rhizobium bacteria.

Cultivation

Cytisus scoparius is widely cultivated as an ornamental plant, with several cultivars selected for variation in flower colour, including "Moonlight" with deep yellow flowers, "Andreanus" and "Firefly" with dark orange-red flowers, and growth habit, including "Pendula" with pendulous branchlets.

Invasive species

C. scoparius has been introduced into several other continents outside its native range and is classified as a noxious invasive species in California, Oregon, Washington, British Columbia and parts of the east coast of North America, as well as Australia, New Zealand and India. These shrubs commonly grow in disturbed areas and along utility and transportation rights-of-way. The prolific growth of this species after timber harvest inhibits reforestation by competing with seedling trees. It is estimated that it is responsible for US$47 million in lost timber production each year in Oregon. In New Zealand, broom is estimated to cost the forestry industry NZ$90 million, and to cost farmers NZ$10 million.

Biological control for broom has been investigated since the mid-1980s with a number of species being trialled. They include the broom twig miner (Leucoptera spartifoliella), the broom seed beetle (Bruchidius villosus), the broom gall mite (Aceria genistae), the sap-sucking broom psyllid (Arytainilla spartiophila) and recently the broom leaf beetle (Gonioctena olivacea) and the broom shoot moth (Agonopterix assimilella).

Eradication

The method used to remove broom is dependent on the prolific seed cycle. Care should be taken to avoid disturbing the ground or the seeding plants between late spring and mid fall. From late fall, through winter, to mid spring are preferred times to eradicate mature plants. There are several methods, cutting, pulling, burning, herbicide or introducing chickens and goats. Often new plants will grow from roots or seed, requiring repeated treatments. Drought areas respond well to cutting while the seed pods are young and still green. In cooler wetter areas pulling is the preferred method and hand operated broom pullers are available.

Phytochemicals

The characteristic constituents are biogenic amines (mostly tyramine in the young shoots), flavonoids (spiraeoside and scoparoside), isoflavones and their glycosides (genistin), as well as allelopathic quinolizidine alkaloids (mostly sparteine, lupanine, scoparin and hydroxy-derivatives), which defend the plant against insect infestation and herbivory (with the exception of the resistant Aphis cytisorum).

Royal symbols

The name of the House of Plantagenet, rulers of England in the Middle Ages, may have been derived from common broom, which was then known as "planta genista" in Latin (there are other theories). The plant was used as a heraldic badge by Geoffrey V of Anjou and five other Plantagenet kings of England as a royal emblem. The "broomscod", or seed-pod, was the personal emblem of Charles VI of France.