Mulberries are of the genus morus and the white and black varieties are native to central Asia. The leaves of the white mulberry are the sole food source for the silk worm, bombyx mori.
The fruitless mulberry was developed from a clone of the white mulberry for the purpose of supporting a US silk industry. The industry never developed but the tree is commonly used in landscaping.
The berries are delicious, the white ones mild and honey-like and the blacks have a richer, fruity but still sweet flavor.
It's obvious why this is not a widespread commercial fruit. The berries ripen slowly and sequentially across the entire tree. The ripeness window is narrow - probably about a day - so daily pickings are required.
When I head for the mulberries with a small container, the chickens race to get there first, jockey for position, and fight for the few that slip through my fingers or fall as I jostle the branches.