Great blue lobelia blooms

This shows, close-up, the lovely blue-violet blooms of Lobelia siphilitica, or Great Blue Lobelia, an Illinois native perennial of the Campanulaceae (Bellflower) family.
 
For more about Great Blue Lobelia and native plants for the Midwest, especially those that do well in shade/moist areas, see the "book" on this website, Gardening with Native Plants in Shady Evanston.