Sisymbrium irio, known as London rocket, is a plant in the family Brassicaceae. It is an annual herb exceeding three feet in height with open, slender stem branches. The flowers are small with four pale yellow petals. The basal leaves are broad and often lobed, while the upper leaves are linear in shape and up to four inches long. The fruit is a long narrow cylindrical silique which stays green when ripe. The younger pods overtop the flowers. When dried the fruit has small red oblong seeds.The common name "London rocket" comes from its abundance after the Great Fire of London in 1666. However, Dr E J Salisbury, in his study of the bombsites of London after the Great Fire of 1940, "failed to find a single specimen, nor has any other reliable observer reported it", according to R. S. R. Fitt