Lobelia siphilitica 'Alba' / Blue Lobelia (White Form)

A later-blooming herbaceous perennial, these flowers can persist into October, keeping pollinators such as bees and hummingbirds well-fed. Lobelia siphilitica grows to 3 feet high, can grow in sun to shade, and prefers moist, wet soil. How about that unfortunate species name? Well, as you may have guessed, this plant was once used to treat venereal disease. This is a rare form of Blue Lobelia that has pure white flowers. 

https://plants.sc.egov.usda.gov/plantguide/pdf/cs_losi.pdf