Last year we had a volunteer Sunflower come up in the yard under a stand of Oak trees.  It was about six feet tall, slender stalk and had a beautiful bloom that you can see if you click on the link above.  This year we had one come up near the house. It is about three and a half feet tall with a thick stalk.   The blooms are similar.  It has been fun watching it grow and the bees are enjoying this early bloom very much.  

Bee on sunflower showing size comparison

Bee on sunflower cropped

Young sunflower closeup