Botanical Prints Artist Carlos Riefel-Where Would I Find Information On Botanical Prints Of R. Yakusimanuml And R. Souliei?

Artist Carlos Riefel-Where would I find information on botanical prints of R. yakusimanuml and R. souliei? - botanical prints

Carlos Riefel was an Austrian botanical artist of the decade to 1940. I have two of his prints and try to determine whether they could be originals or what value should be. One of them is yakusimanum R. and the other is R. souliei. Thanks for any help you can provide.