Banlangen usually refers to the dried roots of a kind of flowering plant in the family Brassicaceae, also known as Isatis tinctoria, woad, dyer's woad, and Isatis indigotica, which are different species but share the same name.

These medicinal herbs grow in many areas of the country. Generally, they are classified into two categories: One grows in North China and the other is native to the south.

China Daily