I have Ilex x meserveae Blue Prince & Princess' growing 5 years now, at the dripline, less than 20' from the truck & they are doing great. I did research before I planted them & know others had success with them also.
They aren't exposed to roots, at least not yet - they are uphill and in a raised bed - but they do get loaded w/ the stems & leaves. The 2nd winter they were in the ground I mowed-up all the walnut & other trees leaves & stems, chopped them fine, and used them as winter mulch.
But mine do require alot of moisture, so be sure your spot is moist.

I'm planning to try Winterberry soon, and I've read that is also very tolerant, but I too would like others opinions.

Thanks artdeco! Mine would be exposed to the roots, leaves, everything, but I think I'll plant them anyway; if yours show no signs of harm from the leaves, stems, and however few roots they're exposed to, I think it's worth giving a try. These hollies are just what I'm looking for, so here goes nothing! I'll post a followup when they are planted.

As an update, I did not plant the 'Blue Prince/Princess' hollies, although, as artdeco pointed out, they will do well under a black walnut. Instead, I planted winterberry 'Sparkleberry' (Ilex verticillata x serrata 'Sparkleberry') and winterberry 'Apollo' (Ilex verticillata x serrata 'Apollo') as a pollinator for the 'Sparkleberry'. I also received a winterberry 'Winter Red' (Ilex verticillata 'Winter Red') from a friend. All of these winterberry holly varieties are doing very well, and even set fruit within the dripline of the walnut. Planted next to them are two spicebushes (Lindera benzoin),a Japanese beautyberry (Callicarpa japonica), and a young black cherry tree (Prunus serotina). All of these shrubs will grow well under a black walnut tree.

artdeco. Good points, and you and I must have a lot in common because I too have planted Blue Prince' & 'Blue Princess hybrid next to a black walnut, having already had success with a standard holly. And I am also toying with the idea of trying winterberry next.

Thanks to all of you for your updates, and for for future ones too. There are lots of ambiguous lists out there for tolerant plants, because of the variety of growing conditions, management, etc.

Water is a major issue under black walnut trees, they are very thirsty! The competition is far to much for a neglected sapling or shrubling. Keep those Messervae hollies well watered their first years as suggested, and during any long dry spell. Water slow and deep, so that the roots really spread out.

Ill take some cuttings (or layer rather) of my blue princess and China girl and try them out under driplinE. I um, planted mine well outside it....lol

A mature walnut creates a perfect dappled shade for so many great plants. Ibe come to really appreciate them. Sweetshrub, spicebush, hemlock, dogwoods, Hosta, bulbs of all flavors, ferns, yarrow, monarda, japanese maple, beauty berry, etc etc. oh carolina silverbell. I’m forgetting some, all planted adjacent to or within drip line. Oh. Witch hazel, itea, .....

I’m also glad to have some acreage without walnuts. But I treasure the one that takes center stage on our front yard. There is more organic matter/humus under that tree than anywhere on my property.

PS I’m ruthless in my quest to secure the walnuts before the squirrels. We have loads of hickories, oaks, and others. But they bury them in my jugLomé (what is with this Hojzz spell check.??.) ok thr squirrels bury them and by the time you see the leaves peeking out, there’s an impressive lateral taproot that seems to never end. I dug one from a sprout on the edge of my yard this summer. It was 12’ Long and up to an inch in diameter. With branching. It is tragically hard to kill those little fu... guys. Another sprouted right in the center of a 20 yo American filbert. How does one surgically remove THAT? I can’t just pull it like any other weed, it would scoff it ripping it’s top off a dozen times over 2 Years. Cutting it 12” below soil? Nooo prob. I believe they would keep up this zombie walnut program until my death — ostensibly a few decades yet -- at which time it would have an extensive underground root system, and could grow a 60’ tall tree within two seasons of me being buried.

Impressive really.