So it's always exciting to run across a plant I've never seen before. I've been watching this one for two years and have not figured it out yet.
It's a small perennial growing out of a limestone slab in a dry creek, so it doesn't get much water. It's in dappled shade/sun and blooms in May as a greenish-brown flower with four petals. Last year I thought perhaps I'd missed the petals and was looking at sepals, especially since they are glabrous, but on closer observation this year this appears to be all it's got.
The most interesting thing about the flower is it only opens during a downpour of rain! It doesn't open when it's just cloudy, drizzling, or lightly raining. We're talking a sky is falling, cats-and-dogs drenching. Is there such a thing as pollination by heavy rain? I haven't seen any creature attempting to pollinate it. As soon as the rain ends, the flower closes again.
My friend Marshall Johnston (Vascular Plants of Texas) doesn't recognize it, and has suggested emailing BRIT.