Hi Jennifer. The non-spreading varieties are the Russian Comfrey cultivars Bocking No. 1 through Bocking No.
21. The Latin name is: Symphytum uplandicum or Symphytum
uplandica. Bocking #14 is one with the highest nutrient density and is the most widely used and available variety as far as I know.
Best,
Aaron

ps: You will need to order or find root cuttings as the seeds of all the Russian (Bocking) varieties are sterile... thus its non spreading nature. However if you have moles or dig near it and accidentally cut the roots, it will grow from even very small pieces of root. So, you only need to buy a few plants and you can make your own cuttings after a season. I have hundreds of plants now and use it instead of compost, just chop and shred the leaves right into the garden beds 4-5 times a year.

Thank you so very much, Aaron. I appreciate the names and the how-to. Just what I needed to know.