|Will White Old Fashioned Bleeding Hearts (Dicentra spectabilis|
|This is one plant I have not tried under a black walnut tree. On one list of plants tolerant of black walnut trees, I found the related Cicentra cucullaria -- Dutchman's Breeches. You might experiment and try one of the D. spectabilis and see how it does. Keep in mind that it will have to compete with the tree for light, water and nutrients as well as tolerate the juglone. Here is the list, it does include a number of different perennials you might be interested in.
I hope this helps.