One of the characteristics of Queen Anne’s Lace is one black flower at the center of all those white flowers. You can see it especially well in this observation (Thank you to @marymarboroughfamily).
Now, in a single flower, or a daisy head, a dark center can help to guide pollinators to where the nectar and pollen are. But that would not seem to be the case here; a pollinator alighting anywhere on the flower platform will find numerous nectar and pollen points. And other carrot-family plants with umbels that form platforms – like fool’s parsley, poison hemlock, fennel, and dill – do not have one black flower in the center, so it isn’t a synapomorphy.
I am left wondering, what is the function of one black flower in this one member of the carrot family?