Wild ColumbineAquilegia canadensis
image by me, Browns Woods, 2010
This plant is not listed at Iowa Plants, but is listed at the Illinois Wildflower and the USDA websites. It's a self-seeding plant, so I usually see it in groups during May. My house has a somewhat shady corner where the columbine enjoys a bit of space all to itself. The foliage is toxic to mammals, so the rabbits, which make up the bane of my existence, thankfully leave this plant alone.
In reading the Native American Ethnobotany, I see that many native tribes used this plant for just about every ailment. I'm sure they were fascinated by the shape of its flowers and heart-shaped leaf lobes.
I've always thought it was very interesting to look at. I can think of other flowers that hang down, but none with the color combination or shape.