Without close examination of the flower parts, it's impossible to say which Commelina, not that I possess such skill. Both are 2-petal blue flowers. C. erecta, a native, is also listed as being present in MI on USDA plants database. Do you have any pics of the flowers open?
If you type 'commelina' in the box, choose that it's the scientific name, check the box for Michigan, you will see both.
http://plants.usda.gov/java/st...
You may be able to decide, but either would be weedy in habit. A good ground cover for moist, shady areas around taller shrubs. Not something I'd allow (either species) in a tended bed of various, well-behaved 'garden' plants.
