There are several species of ruellia that are native to Texas and I'm not sure which one this is.

I don't think I've ever noticed these before - at least not in such large numbers. They were growing in clumps here and there all along the greenbelt. The plants were about a foot tall and look nothing like the dwarf cultivar type used in the landscaping here. If they hadn't been blooming, I would never have recognized them.