Oncidium floridanum and Oncidium ensatum?

Pleurothallis gelida and Stelis gelida
Spiranthes cranichoides and Cyclopogon cranichoides

Sometimes they are lumping (making big genera) and sometimes they are splitting. For me I still consider all Maxillaria as Maxillaria. Not because of being old fashioned but I don't like splitting if the material is still clearly related.

"I searched on Kew for Maxillaria crassifolia but found it accepted as Heterotaxis sessilis."

Justin, isn't this exactly the question you originally asked about? Namely, where can I get up to date botanical nomenclature?

Nomenclature is an ever evolving science. With the introduction of DNA analysis it's become very rapidly moving, but even with traditional morphology it was not static.

Just write your material this way.......
Heterotaxis sessilis(syn. Maxillaria crassifolia). The system is designed to preserve historical information. Any (accepted) previous name is valid just superseded by new (hopefully better) information. You will notice in the history some names that were not properly documented and identified with such info as "nom. illeg."

P.S. My bad, but to be perfectly correct all these names should include the author's name at the end.

I agree with everything Goodgollymissmolly wrote. Even if a name is universally accepted today it might change tomorrow, and many names are not universally accepted. Nothing is ever official and unchanging. You can't keep chasing the best and latest taxonomy - you would never be able to finish writing anything. If you list a synonym you have made it clear what plant you mean. Or if you include the author and year of the citation you have identified the plant unequivocally no matter how it changes tomorrow.

I also agree that Kew is the best single source you are going to find, and as widely accepted as any. If you make it clear that is your reference at a particular time you have also unequivocally identified the plant.

Also, it may not matter for your purposes, but for anyone with an interest in hybrids official current hybrid genus names are absolutely based on names accepted by Kew.

Thanks PMM. Nice to find someone who understands stuff.

Did you leave a "not" out of your last sentence?

No. I did not have any caffeine this morning when I wrote it, so it is awkwardly worded, but there is noplace I would add a 'not'

Well, hybrids of former Doritis and Phalaenopsis are still registered as Doritaenopsis (even though all species have been removed from Doritis) and any hybrid with Trias (an active genus) either with another Trias or with a Bulbophyllum is registered as Bulbophyllum. The Miltonia/Miltonopsis situation is well known with all intergenerics called Miltonia.

So it looks like the sentence should read:

......but for anyone with an interest in hybrids official current hybrid genus names are NOT absolutely based on names accepted by Kew.

I'd be interested in your opinion on this. I think I'm right.

Not a specialist at hybrids at all but I think many are registered under the valid names of the parents at time of creation and most of the time or never changed when the partental names change.

No that's not so Rob. If you register a cross between Phal and former Doritis today it's Doriteanopsis. On the other side...all the Brazilian Laelia/Sophronitis/Cattleya hybrids are now Cattleyas, not just new registrations..all the old ones also. The same for the other examples I posted above.

The Orchid IRA (RHS) makes independent determinations as to follow or not follow ICBN accepted names and when to do so. It makes ICNCP and ICBN relatively different in many cases...and confusing as heck.

I'm doing a presentation that touches on some of these names (though they aren't the main subject) and I like the idea of someone critiquing me here because I don't want to be wrong on anything. I'm 99% sure of myself on the names, but it doesn't hurt for someone to challenge it and thus avoid a mistake. Thanks