Wow, Polygala grandiflora sure looks like the correct answer, the
right ID of the photo I asked about. Many thanks to M. Reed for
the response.

Besides the satisfaction of simply having this intriguing flower
identified, it is interesting to me because I previously have seen
only one species of Polygala, P. brevifolia, and that only in my
yard here in Virginia. I've spent no little time trying to verify
that ID, and am still not sure; last summer, two eminently qualified
botanists visited me to see an unusual flower neither had seen, and
I was getting their input on some longstanding puzzles, and even
though they took a sample of my Polygala home to examine with a
microscope, they were still not able to offer an ID. They said that
the leaves were past the point of being able to clinch an ID.

Thanks again for the help!

-David Cox