Lobelia siphilitica

Lobelia siphilitica, the great blue lobelia, great lobelia, or blue cardinal flower, is a plant species within the family Campanulaceae. It is an herbaceous perennial dicot native to eastern and central Canada and United States. There are two recognized varieties of Lobelia siphilitica, var. siphilitica and var. ludoviciana. Blooming from August to October, it is short-lived, lasting only for a few years. Although self-compatible, a flower is unable to offer pollen to itself and it must be pollinated by insects, primarily bumblebees. Bees use the lower three fused petals as a landing pad. A bee of correct weight will depress these petals on its way to the flower's nectar, this lowers the stigma wiping it against the bee's back....read more on Wikipedia.