Here is a resource I did not see listed above:
http://www.helpmefind.com/peon...
HMF is a volunteer-run site that also has info about Clematises and Roses, so the Peony database is not as detailed as, say, the Rose database...
I work as a volunteer administrator, so I do try to add what I can, but I do not live in Peony Territory, so my contributions are historical; adding references from old catalogs and books that are free online.
It's dangerous work; I have to keep reminding myself that these lovelies would not care much for our hot and humid growing conditions.
Happy gardening,
Virginia