Lunaria Annua, also known as Money Plant and Silver Dollar. I've read that the Pilgrims brought them to the colonies on the Mayflower, and that Thomas Jefferson grew them in the famous gardens of Monticello. Many gardeners consider this plant a pest.The purple flowers in the photos below illustrate how some might consider these a pest.
This patch of ours has grown in just a couple years from a single plant. Now there's all over the area, popping up here and there. It's on the edge of the lawn\wood line so no worries. They look nice too, now and even when they're all dried.