Different varieties evolve because the species is isolated from others of it's kind. Juniper chinensis is a high mountain tree. Under current climate, populations of J. chinensis are isolated on each mountain and have slowly developed different characteristics.
Itoigawa is named because that's the form that grows around the Itoigawa province. Kishu juniper is the form that grows around Kishu area of Japan.
There are lots of other varieties from other mountains and from Korea, China, Russia and Myanmar.
I had not heard of different forms of any of the district varieties but I'm not surprised to hear there are as even in each area, different mountains will have distinct populations that have been isolated for long enough to develop some visible differences.
When I consider the extensive natural range of the species - Japan, Korea, Russia, China, Myanmar - what I do find interesting is that, so far, only Japanese varieties are considered superior for bonsai. I wonder if that's just because we focus on Japan and Korean bonsai growers are happily growing much better J. chinensis bonsai? Is it that more remote cultivars have not yet been tried? Or is it that those few Japanese identified types are really the best of the bunch?
Please note that Juniper species are hard enough to identify. Variations within regional varieties could be a nightmare to identify or pick. Don't be surprised if someone chooses to give an ordinary J, chinensis 'Itoigawa' a new variety name so they can charge big bucks from gullible buyers. Also don't be surprised if standard Itoigawa is misidentified as something new and sold unwittingly.
