Mammillaria neomystax??

A few years ago I sowed Mammillaria neomystax and although the plants are still small I find them very closed related with Mammillaria mystax. In Pilbeams book and on the website mammillarias.net I found that neomystax is a synonyme for Mammillaria karwinskiana ssp karwinskiana. I have my doubts about that. Is this correct? What is the opinion of the Mammillaria-specialists?
I know that giving the right name to a plant is a very difficult matter and that ther are many different opinions, but what do you, specialists, think is the best classification to follow?

Hi Carl,
I haven't grown neomystax myself, but in Hunt's New Review of Mammillaria names he says that neomystax is an intermediate form, linking karwinskiana and mystax, with pale red flowers. Yet in his Postscripts 6, in a list of synonyms, he simply puts it as synonomous with karwinskiana, which is what John Pilbeam uses as his reference. It was described first by Backeburg in 1951 and referenced in Die Cactaceae in 1961.
The description is given as: body simple, to 10 x 8 cm, tubercles 6 x 7 mm, 4 angled; axils with white wool at first and longer bristles. Central spines 0-1, to 2 cm, ascending, brown; radials spines 3-5, to 6mm, white, the upper shortest. Flower pale red, described as approximately 7 x 13mm. Fruit red; seeeds 1mm.
It would be interesting to know on what basis the decision to lump into karwinskiana was taken. From the description is clearly doesn't seem to be karwinskiana, but equally much less heavily spined than mystax. But mystax is very variable, in its own way, as is karwinskiana in its own way too. The original habitat is given a between Tehuacan and Oaxaca, which is a very long way, hardly a specific location. I have seen plants that I consider to be mystax which have considerable variation in their spines along this route, but I was not there in the main flowering time, so can't comment on flower colour.
But to show you some variation look at these two photos, both of which I consider to be mystax. The first is very mystax, from mesa de San Lorenzo, just north of Tehuacan:

and the next which was is western Oaxaca I think has to be a form of mystax as well, at km 113 on Mex 190 from Oaxaca to Huahuapan de Leon:

Personally I would think that the closest relative to mystax is not karwinskiana but carnea, which also is abundant in this area. It could well be that a pale red flowered plant might be a carnea form, or just one of the many variable forms of mystax.
Keep the seedlings growing, Carl, I'd like to see one!

Chris, thank you for the reply, very interesting, especially the photographs and I promise to send pictures of the seedlings
but my question remains..what do you do when you have to choose between the "old" and the "new" names for example "neomystax" or "karwinskiana ssp karwinskiana." in other words, wich classification is in your eyes the most correct or the most usefull?

My own preference is to go with the version Hunt that is in Pilbeam's book, simply because it is the book that I have looked at most, so I recognise it, and so do most of we Brits. I have also looked at Luethyi and Reppenhagen, and find Luethyi close to Hunt in many cases, but Reppenhagen seems to take rather small differences into account when he depicts a species, and I find that a bit too much in many situations. I find the New Cactus Lexicon a bridge too far, as even more consolidation of species has been done. Because there are no universal rules on what degree of difference is significant and should lead to definition of a species or subspecies, every botanist and plantsman is going to prefer their own view of life. So there are no rights or wrongs, just what one feels comfortable with.
But when I write my labels I write them as, for example:
Mammillaria karwinskiana ssp collinsii R677 'tropica'
So while I follow the Hunt classification, I recognise that there are different forms, ideally by adding the field number, and then if that field number plant was described under a different name, then I put it in also in quotation marks. The experts in nomenclature would say that this 'tropica' is actually a cultivar name and should be started with a capital T, so 'Tropica'. But I just don't like the look of that, as it was not described with a capital t.
This way, I can see from the label where the plant fits, but also know that it was described differently to start with. I also arrange my plants in their series and groups, so again I can see affinities and differences more clearly.

Hello Carl,
At the moment there are 3 more or less valuable classifications of the Mammillaria genus. Reppenhagen, Hunt and Lüthy.
The choice is all yours wich one you like to follow and feel most comfortable with it. Hunt is known as the arch lumper and Reppenhagen as splitter, although he have reject much old names like neomystax too (he put it in mystax). On our last trip to Germany, you have seen with your own eyes how many differences there are between some lumped plants.
In my case I use Reppenhagen, which is for me the most correct classification and he has a field experience of more than 30 years with almost only Mammillaria.