Here are some pictures of Morus Nigra “Black Beauty” which I bought from https://www.whiffletreefarmandnursery.ca/how-to-order/#page30 last Spring. It is listed by the nursery as Zone 4/5 Self-Fertile, and I am sure it is hardy to Zone 4 because it is grafted on Morus Alba Tatarica.
It survived first Winter here in Toronto (zone 6b). In Spring I didn’t notice any dieback, all branches were alive and pushing out buds. I believe I didn’t water it enough, hot sunny days in April and still frozen ground, and I lost alive branches.
I believe it is Morus Nigra. It had few fruits this year, looking exactly as in pictures.
Two nurseries in Ontario sell grafted “Persian” mulberries; one nursery in British Columbia were advising me “it won’t grow in Ontario!” referring to some not-so-authoritative sites such as Daves Garden.
I shared more pictures at Google, https://photos.app.goo.gl/dse9K1h87613qSwM7
P.S. Perhaps all “Persian Beauty” or “Black Beauty” in North America are the same DNA, propagated by grafting. I bought two plants, and both plants came with freshly cut-out branch from it, perhaps nursery used it for propagation. Cutting out branch, and then selling. Absolutely sure this nursery doesn’t grow it from seeds