These are mushrooms on my front lawn that are known as "Fairy Rings". I read about these in the local paper last week. Apparently they grow in a semi-circle like this for some unknown reason. The theory is that they grow from fungus from old dead trees and a very wet rainy spell, or from fungus from fertilizers or other chemicals spread on the lawn. I have no idea. They just appeared this year. There are no old dead trees around so what's your theory? Any mushroom fans out there?