Ruellia simplex - Broadleaf Bluebell

Ruellia simplex—frequently referred to as the Broadleaf Bluebell, Mexican Bluebell, or standard Mexican Petunia—is the parent species of the pink 'Chi Chi' variety you just looked at. While 'Chi Chi' provides softer pastel pink tones, the standard wild type is famous for producing deep, metallic blue-purple, trumpet-shaped flowers. 

At a pond's edge, this plant behaves as an incredibly hardy, fast-growing marginal or bog plant that adds rich, dark color and reliable vertical structure.