I agree with Ashley. This looks like a wild petunia (Ruellia sp.). Usually the flowers are a purple; white flowers are unusual.
The USDA Plant Database lists 5 species for Oklahoma (all of which occur down here in Georgia).
To identify to the species, you'll need information on the flower tube and the leaf shape etc. If the leaves directly below the flower belong to the flower, this may be the Fringeleaf Wild Petunia (Ruellia humilis) - but you'd need to confirm.
For the developers at New York start-up Networked Organisms, smartphones are the butterfly nets of the 21st Century. Their tool, Project Noah, lets people upload photos of plants and wildlife around them, creating a map of the natural world and contributing to scientific research in the process.
Bespectacled scientists of yore would carry around hefty field guides, made up of hundreds of pages of text and photos. But these days, smartphone owners have a lighter option: an app called Project Noah, which aims to help people identify plants and animals as well as collect data from "citizen scientists" about where certain species are located.
Project Noah enables us to be part of a more focused online community where we can learn more about wildlife around us and contribute to scientific research. It pulls participants into deeper, more meaningful engagement by enabling people to go on “missions” to collectively map changes based on sightings.
A modern invention that may also hold the key to saving species in the future. Project Noah is a global study that encourages nature lovers to document the wildlife they encounter, using a purpose built phone app and web community. In addition to the virtual "collection" of species, Project Noah encourages citizen science by linking up with existing surveys including the International Spider Survey and the Global Coral Reef Monitoring Network.