Common Evening PrimroseOenothera biennis
Photo by me, Pleasant Hill, near GC1FWQJ Groovin' with (dd) (archived) and GC1FWQ1 Hickory Plaza (active).
I see this plant frequently in "waste" areas. It's native, and very upright. Height varies greatly. The flowers are located at the top of the stalk in a cluster, and remind me of balloons. They are wide and open with a pinched neck, like a balloon.
I photographed this on a windy day, so I refer you to Illinois or Wisconsin's wildflower websites for a photo of the entire plant. I had to hold the stalk just to get this photo.
Evening primrose is currently used to aid various health problems as noted all over the internet, including here and here.
