Spartium junceum is a vigorous, deciduous shrub growing to 2–4 m (7–13 ft) tall, rarely 5 m (16 ft), with main stems up to 5 cm (2 in) thick, rarely 10 cm (4 in). It has thick, somewhat succulent grey-green rush-like shoots with very sparse small deciduous leaves 1 to 3 cm long and up to 4 mm broad. The leaves are of little importance to the plant, with much of the photosynthesis occurring in the green shoots (a water-conserving strategy in its dry climate). The leaves fall away early. In late spring and summer shoots are covered in profuse fragrant yellow pea-like flowers 1 to 2 cm across. In late summer, the legumes (seed pods) mature black and reach 8–10 cm (3–4 in) long. They burst open, often with an audible crack, spreading seed from the parent plant.
The plant is also used as a flavouring, and for its essential oil, known as genet absolute