Posted: 13/07/2016 at 12:55
So much depends on growing conditions. I should think it's near impossible to tell one from t'other as with many cultivars.
Unless you buy from a reliable source that can confirm the tree has been grown from cuttings/graftings from the original cultivar. No chance. Add in the fact that some suppliers don't know or care about the origins and may be selling seedlings from a named cultivar ( a seedling is never the cultivar however much it may look like it), then the chances reduce even more.
Tell your friend it's not a hybrid, hybrids are a cross between two species. The named varieties are all cultivars Cul(tivated) var(ieties) of one species, Morus nigra.