[Wikipedia] Probably originated 4000 to 6000 years ago in the Hindu Kush are: The origin of B. rapa, both geographically and any surviving wild relatives, has been difficult to identify because it has been developed by humans into many types of vegetables, is now found in most parts of the world, and has returned to the wild many times as a feral plant. A study of genetic sequences from over 400 domesticated and feral B. rapa individuals, along with environmental modelling, has provided more information about the complex history. These indicate that the ancestral B. rapa probably originated 4000 to 6000 years ago in the Hindu Kush area of Central Asia.... (link added by Suzanne L. Weakley)

This species is native to Eurasia, but has spread all over the w: Field mustard is an upright winter annual or biennial that is a member of the mustard family (Brassicaceae).... This species is native to Eurasia, but has spread all over the world and is now naturalized throughout much of North America. It grows from sea level to 5,000 ft..... (link added by Suzanne L. Weakley)