I am growing all three species (M. alba, M. rubra, and M. nigra). I don’t know the basis behind the scientific naming, but my M. nigra trees can be distinguished by their noticeably larger, black-colored buds. I am not a mulberry expert, but based on my limited experience, if I were trying to characterize an unknown mulberry, the buds would be the first part I would examine.
I would be curious to see if this purported white-fruited M. nigra has large black buds (like other nigras) or smaller, light-colored buds like albas.
The original scion source for this cultivar labeled it as M. nigra, probably as an advertising gimmick. It was then introduced to the wholesale trade and purchased by retailers – including One Green World.
Inspections of morphology and more recently cytology have demonstrated it is not. Several of us have pressed OGW on this point. So far they’ve modified their description to indicate this but have left confusion in the latin name.
This has been a better response than other retailers, who reject the idea that the wholesaler could be wrong, in favor of offering a plant labeled M. nigra.
Ditto for seed sellers. I sent ploidy test results to Sheffield’s showing that seedlings grown from their alleged M. nigra seeds were diploid, but they still have them listed that way. Though I haven’t grown out their seeds from India (latest batch) yet, the ones from Hungary are definitely not nigra.