The bitumen pea is a common flower of fields and wastes and it can be a troublesome weed. The name comes from the tar smell when the leaves are crushed. The flower heads and trefoil leaves resemble clover but the fruits of P. bituminosa are in the form of pods and the plant belongs to the pea family. The flowers are held on thin, stiff stems which can be very tall. It flowers from spring till summer with a second flowering in autumn.