[Campions and Catchflys: The Genus Silene West of the Cascade Mountains of Oregon and Washington]
Bladder Campion, Evening Campion, White Campion
Silene latifolia
Synonyms: Lychnis alba, Silene alba, Silene latifolia ssp. alba, Silene pratensis

White Campion: Note the inflated sepals.
Paul Slichter