M. nigra is a bush of the genus, and not from the north American or east Asia continents.
The Black Beauty cultivar sold on Russian Mulberry (Morus alba) rootstock grows every bit as fast as M. alba in my location. After having it in the ground for about 1.5 years I cut it back to 4 ft. a few weeks ago. That only made it mad 
. My wife does not care for the taste of the fruit so I’ll be digging it up and giving it away to anyone who’d like to come get it. I do not ship plant material.
