Here's another weed that is common in the Chicago area and that grows in my garden. It is called the Asiatic Dayflower and has a true blue color. This is another weed that holds a lot of memories because as a kid we called it "Mickey Mouse flower" because of the two blue petals that sit atop.
Our childish sobriquet glossed over a pretty invasive weed that was possibly introduced into North America as an ornamental plant in the garden. It has been growing on our property ever since I can remember and no amount of weeding has kept it from coming back. Which isn't really so bad because it grows in the shady areas and doesn't seem to spread. It forms a nicely dense border at the bottom of the stairs and along a walkway. This particular bloom was growing right below the orange daylily I posted previously. Like many other weeds this one is pollinated by bees but the leaves are a food favorite of the Six-Spotted Beetle and White- Tailed Deer-neither of which I've ever seen in my garden. The dayflower gets it's name because the flowers are short lived. The Wikipedia entry on this plant states the plant's genus name (Commelina) is derived from the Kommelijn family who had three sons, one of which died at an early age. The dead child is represented by the lower petal of the flower that is white in the Asiatic Dayflower.
I found this an interesting gardening tidbit but can't find any info on the Kommelijn family on Google.