Common broom (Scotch broom, broom)

Cytisus scoparius

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 trifoliateleaves 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.