Rats - I was hoping to stump the botanists! Good call, Scott. Yes, it's a remontant bloom of Oxalis violacea wihout leaves. In fact, if you zoom in on the picture, you can see oxalate deposits at the tips of the sepals on unopened flowers. These can also be seen in the notch on the emarginate leaflets when they are present. I would like to know if remontant bloom on this plant is always scapose (a flowering scape without leaves).
The plants are flowering at Fred Rose Park in Hobart, Indiana, where Sandy O'Brien is doing an EXCELLENT job of restoring the savannah with prescribed burns. Two of these plants were discovered on a dry clay slope in partial sun. Photographed on 8-12-2010.