On my run this morning in Freeland, Pennsylvania, I spotted one of the plants of my childhood. The Common Tansy, a native of Europe, is an invasive species in the USA. It is so common that I thought it was native to my hometown in Michigan as we saw these all over the neighborhood growing up. We used to pick off the hard flower heads and throw them at each other.
There are efforts by conservation agencies in the USA to stop its spread. The plant is common in Europe. It is toxic to livestock and animals and severely reduces biodiversity and suitable habitat for local American animals. Tansies have been known throughout history for their medicinal properties and were used by the Romans among others. It was brought to the USA early, 1600s, by the first settlers for planting in the garden, as it is known to repel ants and other bugs. It spread throughout the northern USA quickly, and made it to Michigan in the 1860s.