Hello again, Guido:
Just some counterpoints; having some fun!
Best wishes,
Vic
It is however useable to differentiate between the genera of the slippers (and that is what we are talking about, the differentiation between Mexipedium and the othere genera of the slippers and not the differentiation between the various species of phragmipediums.)
Well, if inflorescence branching isn't constant within Phrag, then it doesn't discriminate Mex and Phrag perfectly -- if a novice compared Phrag caudatum with Paph and Mex based on this character, he might group Mex with Paph. Throw in a branched-inflor. Phrag, and the situation becomes more complicated.
You know that staminodes are variable within a number of species (for example very much so in the brachypetalums). But there is no staminode in Phragmipedium that can be confused with the staminode of a Paphiopedilum.
Again, it is true that staminodia of Paphs and Phrags are dissimilar at the gestalt level, but those of Mex and Phrag are not particularly! Again, overlapping suites of characters can make identification -- using keys -- difficult for non-specialists.
While I am at it: plant size
Yes, that is no good within any given species and no good in many other cases. But within the slippers, it is an excellent criterion to differentate between Mexipedium and anything else.
Come on now! What about Paph barbigerum or helenae? To be picky, we could even throw in some of the tiny Cyps. True enough, the leaves of Mex show xeromorphic adaptations, as do those of Paph druryi. So, again, we need to say 'very thick-leaved plants that are very small, X cm by X cm'.
The same applies for leaf texture. The same for flower size, the same for overall flower morphology, the same for flower colour.
These features are mostly in the realm of gestalt! For the first, compare Paph druryi with Mex, for the second, compare Paph hangianum with Phrag kovachii, for the third and fourth, maybe get confused between Paph delenatii and Phrag schlimii. You and I can tell the difference, but a practical system is one that suits multiple users of different backgrounds. *Not that I'm saying we shouldn't have a system with separate Paph, Phrag and Mex* -- only, as the Devil's Advocate, that one genus is an alternative, based on the bulk of the character data that supports a conduplicate-leaved lineage more than it does the specific 3 genera.
But you will have to grant me that founding a taxonomy on DNA studies is not exactly practical (besides the fact that it does not work). Or maybe you can ask how many people of the somewhat 35000 members of the Orchid Societies world wide (admittedly a rough estimate) have access to a lab in which they can do molecular biology.
I won't grant you the first one in its entirety, Guido. Nobody doing molecular phylogenetics works with entirely unknown groups of plants; i.e., virtually all plants studied have already passed through the alpha phase and (hopefully) have valid names and fall into somebody's classification. Molecular data, as applied to such plant groups, can be very useful in determining whether supposed plant taxa have a single evolutionary origin, or several. The latter was found to be the case with Flacourtiaceae some years back, and after morphological/anatomical investigators took a second look, they found decent characters that support the separate origins. So in this case, molecular phylogenetics helped to redefine a plant family, since the 'true' Flacourtiaceae group could only include those plants related to the type species. Now, the taxonomy of former Flacourtiaceae groups has been changed, and accepted by most taxonomists. For *many* similar examples, please flip through Peter Steven's Angiosperm Phylogeny Website --
http://www.mobot.org/MOBOT/Research/APweb/welcome.html . Of course, similar stories exist within the generic level.
So far as practicality goes, the members of orchid societies don't need to do this work! Results are easily disseminated, and when taxonomy might change as a result, implications for morphological diagnoses can be well elucidated. Who would suggest using direct molecular research to identify that non-blooming Paph plant on your windowsill, just collected (illegally, maybe) in Borneo? Let it bloom first! Then, if it doesn't match other species' descriptions or photos, bring it to the attention of a specialist or two. Then, maybe it'll get described and put into a taxonomic system. Then somebody might want to do molecular work to see what species it might be related to (genetically). Just an example.
And I maintain, that if we can differentiate between certain plants and plant groups by looking at them with the naked eye, it is very unpractical to blur the issue by anything else.
OK again, but let's talk about forming a classification that has a key. That's the issue so far as I'm concerned. And remember, I don't object to Mex, Paph, & Phrag -- since they can be keyed out, AND they form separate evolutionary groups! (so long as you are willing to consider a monotypic genus a group)
I know of no instance within the study of slipper orchids that molecular studies have revealed anything that was not recognizable with alphataxonomic means.
Come on now! Molecular phylogenetic research has, e.g., cleared up the issue of whether the Paph delenatii group (Parvisepalum, at whatever hierarchical level) is distinct from the Paph concolor group (Brachypetalum/Concoloria). Different taxonomies exist, but this research has shown that the 'parvisepalums' and 'brachys' branch off sequentially from the base of Paph, such that one subgenus or section for both would not constitute a natural group.
And if one gets picky with your usage of the word 'study', molecular research has certainly helped us to understand floral evolution among the slippers. Given that Paphs and Phrags at the base of their respective sub-trees have infolded (and usually inflated) labella, that Mex also does, and that Cyp (for the most part) and Selen also do, one can readily infer that such floral morphologies are 'primitive' within Cypripedioideae. This has consequences when one tries to interpret the gestalt floral similarity between, say, Paph delenatii and Phrag schlimii. Cribb hypothesized parallel evolution based on pollinator similarity, but molecular phylogenetic studies suggest this (basic) similarity to have been derived from shared, primitive characteristics. The Lorifolia Phrags and the vast majority of Paphs are more evolutionarily 'advanced'. Interestingly, the phylogenetic tree strongly suggests that the evolution of fly pollination has occurred several times in parallel among the slipper orchids, from basically bee-pollinated flowers.