The official register of Hybrid names is the RHS Database of Hybrid names. Do not know how many registered hybrids there are.... 40, 50 60 Thousand???? and within each crossing (Grex) there are infinite variations.

The latest accepted species name is kept in the Monocot register which i have never viewed and do not know how many entries it contains.

Other resources are go to google and select images, but beware, lots of errors in names there. Books. I have "What Orchid is That" which has over 1100 species illustrated and identified. But that book may only be available in Australia.

So, the problem is the immense amount of data and usually once that hybrid tag is lost another Noid is created.

You might find this site good for species ID

Here is a link that might be useful: http://orchidspecies.com/indexc.htm

I don't know of any dichotomous keys for hybrids as there are so many hybrids out there. Finding dichotomous keys for orchid species is hard enough. We might be able to direct you to more references if you let us know which genera you are interested in. For Phalaenopsis, the book by Christenson is excellent. For Catt alliance species, the book series by Withner is also excellent. All of those books have dichotomous keys.

Many thanks :) In fact, I can only find the latest version of "What Orchid is That" in a australia-only delivery. There are older versions available on amazon.co.uk though. "The Illustrated Encyclopedia of Orchids" seems good also.