When I first noticed this flower in Damascus, PA I called it Airplane Flower, since the bloom resembles an airplane with wings and propeller. Since then I have noticed it as a dominant, though small, under-story flower. These photos are from yesterday in Glen Spey, NY.
I have not encountered anyone who uses Fringed Polygala as a medicinal, though according to Iroquois Medical Botany by James W. Herrick it was considered a powerful medicinal plant by the Iroquois. Such classification was based on the strength of the medicine, how or where it grew, and the nature of the illnesses it cured. Fringed Polygala attained status as a powerful medicinal by nature of it being evergreen and because of the diseases it was used for (including that some of the illnesses came from settlers).
This is another example of a common herb that has been largely forgotten by herbalism. We disregard it, while the Iroquois formerly classified it as a powerful medicinal plant. Of course, one question is whether the population would be so abundant if we did desire it for use. It's relative abundance in our forests indicates some toxicity, as the deer are leaving it alone. I have not observed them eating it, but perhaps they do nibble some. (Toxicity, as alluded to above, is also a criteria of Iroquoian powerful medicinal plants.)
Ranunculaceae, the Buttercup Family, is treated by Rhoads and Block (The Plants of Pennsylvania) first by flower symmetry - bilaterally symmetric or radially symmetrical. If radially, then based on leaf arrangement. Opposite leaves are of Clematis (Virgin's Bower); otherwise they turn to fruits and then flower colors (which is reverse of growth order and a little impractical for a key being used in the field). Anyway, Ranunculus is known by the shiny yellow flowers, such as those held up to chins to determine if one likes butter. Though a strange practice, I have found it to be true. As I child I enjoyed butter and my chin reflected the yellow of the flower petals. Now that I have lost my taste for butter and grown a beard you can no longer make out a reflection from the flower. There are several kinds of Buttercups, and the family contains several other very important genera such as Aconitum, Anemone, Thalictrum, Hydrastis, Coptis, and Actaea.
In case some of the above does not make sense, I will be exploring the details later. These pictures are from yesterday a Buttercup by the river and below an image of Marsh Marigold is included.