aka pukeweed; Lobelia inflata; Campanulaceae (bellflower family)
This eastern North American native forb grows to about three feet tall in partly sunny areas with moist soils. The flowers are about 1/3″ wide. The internet is full of interesting claims about the medicinal uses of this plant; some sources simply state that it’s poisonous and shouldn’t be used at all, while others note its use by Native Americans for a variety of purposes, including treatment of respiratory ailments, as an emetic, and as an entheogenic (go ahead and click, I had to look it up, too).
For more on medicinal uses, including current practices, check out the University of Maryland Medical Center page.
The next photo shows what I call the “five foot view”: this is what I see when walking along (my eyes being about five feet above ground level).
One little spot of color and I’m down on my knees having a closer look. Shame about all the Japanese stiltgrass, though.