Descurainia pinnata is a species of flowering plant in the family Brassicaceae known by the common name western tansymustard.

It is a hardy plant which easily becomes weedy, and can spring up in disturbed, barren sites with bad soil.

This is a hairy, heavily branched, mustardlike annual which is quite variable in appearance.

This tansymustard is toxic to grazing animals in large quantities due to nitrates and thiocyanates; however, it is nutritious in smaller amounts.

The seeds are said to taste somewhat like black mustard and were utilized as food by Native American peoples such as the Navajo.