Unfortunately Silene latifolia is another night blooming flower--it did open somewhat when shade hit it later in the day, so I was able to identify it without risking yet more mosquito bites. I think its cousin may have been across the street, and I thought it was the same flower--Bladder Campion differs from White Campion, or "evening lychnis," as it is also called, in that Bladder Campion is open during the day, blooms on taller stems, and has smooth leaves and upper stem.
Learn to identify one hundred species of flora within walking distance of your home! scsours began this challenge in July of 2008, and I was eager to hop on the bandwagon about a month later. I've remembered much and learned even more. It's been a fun but slow process. Spring has finally arrived here in Massachusetts, and I will hopefully be posting often soon.