Chicory (Cichorium intybus) is another common weed found in Chicago. It can be spotted growing alongside roads and in empty lots throughout the city. It is a bushy perennial that is native to Europe but has naturalized in North America. In Europe it has a very long history as an herb with various uses in the kitchen and as a medicinal plant.
The blue hue of the flowers is actually much nicer in person. One time I spotted a pink- colored shrub growing between two blue flowering shrubs near an on-ramp on the south side of Chicago. I like the flowers so much that I've taken cuttings to use it as a cut flower but the cuttings wilted before I put them in water. I haven't noticed any butterflies or other beneficial insects attractd to these and a Google search doesn't give any info. This particular plant was growing near the other weeds I've recently posted.