What's That, You Say?

The first assignment for this week was to find something that is "unknown" to me and to provide clues about it so that others may be able to identify it.  Sometimes our "unknowns" are easy for others to identify; other times, we may need to consult our field guides.  So here is my unknown...

 

I found this in my backyard, however, I have seen them growing in pastures.  As you can see, the purple flowers are rather small, but the entire head of the plant is larger in size.  These two pictures only show two of the plant, but they were growing all over in groups, or patches, mostly under the hickory trees.  They weren't there just a few days ago; they seem to have sprouted quickly after the rain we've had during the last couple of days.

 

So.....  What's your guess?