While I was pruning back my spent spiderwort plants, I found an unfamiliar plant that I cannot id in any of my dozens of wildflower books or anywhere online. It may very well be considered a weed, but beauty is in the eye of the beholder and I am inclined to let it grow if it is not noxious. This is an herbaceous plant about 1-2 ft. in height with whorls of trifoliate leaves. The solitary, one inch flowers are pale yellow with a deep purple center and protruding stamen. The five petals are fused into a flat saucer shape that hangs "upside-down" from a long petiole that projects from the stem where the whorls of leaves grow. Anyone who could give me some idea would be most appreciated.