Psychopsis ID question to "the experts" ;)

[kavanaru]

Psychopsis papilio, Psychopsis sanderae, Psychopsis krameriana, Psychopsis latourae, Psychopsis versteegiana, Psychopsis Mendenhall, Psychopsis Kalihi, Psychopsis Mariposa, Psychopsis Butterfly, etc...

All are gorgeous plants... but... how do you recognize Who is Who? I mean, most of them look so similar, and sometimes (I have the feeling) the pictures in internet are mixed up...

Is there any link to a "serious" website, with hint for their identification? or does anyone knows which are the differences?

I just receive today a Psychopsis ??? var. alba. I forgot to ask the man at the nursery which species or hybrid it is (no label, but am sure the man knows very well which plant it is ) We were just having a nice long chat, and I forgot to ask.. so, I decided to check in internet and try to give a guess, before calling him tomorrow to ask... and wow! that seems almost impossible to me!