I do not have a picture. I think it is a perennial flower. I believe it's very common. The name starts with an "A". Has a tall stem and at the top has a very broad flower. I know that there are white blooms but maybe they have other colors as well. I live in Minnesota.
If you don't have a picture, you're going to have to give a little bit better description--can you say more about the shape of the flower, what the leaves look like, etc?
Aster, Achillea, Allium, Asclepias, Echinacea (sounds like A). I can think of lots more. Is the bloom a disk, spike, etc? How big are the leaves. How tall?