But we've had one little odd cactus on the place that I'd never caught in flower...until this year. Bright yellow, but with a wine-red center and staining up the centers of the petals, so it looks like a tulip, almost. According to two of my reference books, it's a red-eye prickly pear, and the catch is that the red-eye prickly pear (in three races) is found from Arizona to west Texas...west of the Pecos River, not on the east side of the Edwards Plateau.
So this little beauty is a sort of mystery. In its general description, it fits the big Manual of the Vascular Plants of Texas model of the red-eye prickly pear...details of the pads, as well as the flower. But...what's it doing here? It's not on a roadside, where seed might've fallen off a truck with a load of cow manure or something. There was never any structure anywhere near where it is--the land went from prairie to plowland to pasture--so it's not likely to have been deliberately planted (not since pre-European-settlement times, anyway...I suppose an Indian tribe that ranged to the west side of the Edwards Plateau might have found some and brought back fruits or seeds, but that's a long time ago.)
I've asked for help from professional botanists.