Here is the unusual weed of the week. It came from an Ames lawn. It looks like Ground Ivy (creeping charlie) except it does not have a square stem and does not have the mint odor. Also, it is spreading by underground rootstalks and not above ground runners.
It is Creeping Bellflower (Campanula rapunculoides). It is an escaped ornamental that has become an invasive weed. It has a blue, bell-shaped flower at some times of year, but in mowed conditions may go most of the season without a flower.
It is hard to kill. It is resistant to 2,4-D and many of the other common lawn herbicides. You will need something with Dicamba in it and it will still likely take several applications. Luckily, it is rare in Iowa.