What is this plant?

My Heartland Community College class, on how to design an ecologically sustainable yard with native plants, begins tonight! Getting into the spirit, I can't wait to learn what this amazing flowering plant in our yard is called. I know that it is native to our area, since it is planted at our neighborhood elementary school's native plant garden, and I see it all over Founder's Grove. During most of the summer, the flower part of the plant is a light green, barely looking like a flower. But then in late August and September, the green turns to a beautiful red, then dark red, attracting all the bees in its vicinity.