This small bush is in the mallow family; it has ragged-edged heart-shaped leaves, and bright golden flowers. I think it may be Bastardia viscosa, except its flowers are a little orangier (than some pictures) and it's supposed to live almost 400 miles away in extreme South Texas.
This beauty is in the genus Mirabilis, in the Four-o'-Clock family. Those vivid magenta petals are open for only a few hours--easy to miss if you walk by it at any other time of day on the day they're open--so usually what you see are the papery bracts, translucent and lightly touched with pale pink. It flowers after rain, from early summer through, obviously, now, and in a wet year may stand 3 feet tall or more. In a dry year, like this one, it's barely knee-high. This plant with no petals visible was IDed for me as M. albida, but the vivid purplish-pink of the petals makes me think it might be M. gigantea. When I first saw it from the tractor, it had more of its petals on; by the time I'd parked the tractor, fetched the camera from the house, and walked back out to it, most had fallen (it was evening.) It's an original prairie plant, and it seems to be spreading to different areas of the prairie restoration project.