This is the Royal catchfly (Silene regia), a wildflower species that is threatened in Arkansas and Indiana, endangered in Illinois, Kentucky, and Tennessee, and critically imperiled in Georgia, Ohio, and Oklahoma.

In Missouri, it's merely classified as "rare." It is found only in the Ozarks. They were uncommon but not difficult to find along the Ozark Trail in early May 2008. They normally like open and disturbed areas but I found them mostly in woodlands with light undergrowth.

See the Center for Plant Conservation for more information on status.