The RHS as well as ITIS are both recognised authorities Myriam, sometimes you will find a species on both or either. ITIS seems to only list species.
I can't say whether the RHS updates regularly, they may not have updated this particular species because they don't accept the changes. If you search for any of the given names it always takes you to Podophyllum delavayi. I guess that is what we should be using.
http://apps.rhs.org.uk/rhsplan...
Always beware names given by sellers, some will use a different name in order to make the buyer believe they are getting something different so it's a good idea to check out both the RHS and ITIS if it's not in the RHS.
It's always a good idea to search just for the genus in some cases, here's a list for Podophyllum ..
http://apps.rhs.org.uk/rhsplan...
