As you can see from the picture, the blooms on one of my 'Magnus' coneflowers appear to be forming multiple tiny blooms. It looks similar to a hen-and-chicks succulent. These blooms show no tendency to turn color at all. So far, only one plant is exhibiting this trait. I believe this plant came back from the roots because seedlings that came up this year are a lot smaller than this plant. I have done nothing different regarding this plant from prior years. Has anyone else experienced this and does anyone know what causes it? If nothing else, it just proves you can't predict what will happen in the garden!
Is my 'Magnus' coneflower mutating?
I think it's the disease aster yellows. Here are some links.
After looking at the links you provided, I think you are right. Have never seen anything like this before and this is the only type of plant that is affected in my garden. I am removing them. Thanks very much for your help.