Tansy is a perennial flowering plant in the aster family, native to Europe and Asia. but thrives in North America, probably introduced by the settlers arriving from Europe as long ago as the 1600s. In some places is considered a noxious weed. It's also known as Bitter Buttons, Golden Buttons or Cow Bitter.
It's had many medicinal uses including treating worms, digestive problems, fevers, rheumatism and measles. You can even use a solution of Tansy as a face wash, or bathe in it to ease joint pain. It has been used as an insect repellent, and it was packed into coffins, wrapped in funeral winding sheets, and Tansy wreaths were laid on the dead. It can also be used as a dye. A useful herb indeed.
Tradition says that if you plant it by your kitchen door, you will never be troubled by ants in the kitchen.