there is a family of vines called malphigae (may have spelled that wrong)- which resemble ayahuasca, and are even more poorly understood, but are to be considered part of this "new ayahuasca family" of plants which is ONLY JUST NOW coming to light.
Actually, the whole genus 'Banisteriopsis' is in the Malpighiaceae family...as is the genus 'Diplopterys'. As a result of taxonomic revisions, in 2006 a number of species were moved from from Banisteriopsis to Diplopterys.
This revision is the cause of at least one, imo, widespread misunderstanding on a few threads I saw at the ayahuasca forum, where it appears people think they are discussing two plants, but are in fact using an accepted name and a synonym of that name. They may really mean to be referencing two plants, but with the latin names they are using, they are only referring to one.
I've been meaning to put more work into actually creating a more solidified list of accepted names and synonyms based on the literature but I'm pretty crunched for time at the present. I was hoping to compile it and then upload it, but as this thread now exists, perhaps I'll just upload it piecemeal before compiling it.
A final note, as endlessness points out, the sources for much of this info are rather shaky. Ratsche published certain things (specifically on B. muricata and B. caapi) that are impossible to actually trace back to their source (in the case of the B. caapi varieties, it's a D. Mckenna lecture that no one has any evidence of and a topic and a name that were never published on or published as good varieties by D. Mckenna, raising numerous questions). However, despite the lack of solid grounding, the caapi info (and I believe the muricata info as well) have made it into numerous places (wikipedia, forums, etc) as fact.