No idea Richard, its advertised in several english nurseries as morus nigra AGM, usually british nurseries have AGM, Chelsea/king james and Carlton House
" Cultivar Selection
There are a number of black mulberries to choose from;
Morus nigra AGM: the species is highly recommended, is widely available and an excellent performer in terms of fruit production and as an ornamental tree.
Morus nigra ‘Chelsea’ (syn. ‘King James’): a cultivar of great historical interest, originating in the Chelsea Physic Garden, London. Fruit is especially large and succulent with an intense, rich flavour. It can be eaten fresh, in preserves or made into wine."