Lumping v Splitting; fine white spined Mammillarias

I have been wondering on why some genera are split so much, while others arent. For example, Hunt combines tons of rebutias into single species, many of which look quite differnt. Yet mamms seem to have stayed more split, tho I am sure some of you think more lumping than there should be.
For example, here are four of mine, lablled from top left clockwise albilanata R783, humboldtii, herrarae and supertexta. Herrarae hasn't flowered, but I gather it has red flowers So 4 white spined, red flowring mamms, yet 4 species.

Interested in your views, re your choice, and also
1. Why the difference re Mammillarias and Rebutia. Is it that the Mamm poplulations are more distinct in the field, that is, you don't find supertexta mixed up with albilanta, while the various forms of Rebutia fiebrigii appear together. Or is it somewwhat to do with the fellow that did the field work, and his/her views of species.
2. What about humboldii v herrarae. Pilbeam shows 2 forms of former, and one has same floer as herrarae and he says it resembles it. I gather they grow fairly near each other, tho with his map, I cna't tell i that is 50 or 500 kms apart. Is it just they are in different, tho somewhat close, locations.
3. are they labelled correctly. I wonder about supertexta, I found this pic I had taken, so.....

Chris
There are many, Mike, that really do think that the lumping in Rebutia has gone too far. But let me pass on that debate for now and on this Forum at least.
In general terms, I think what you are actually asking is "what is a species". Over the years botanists, field reasearchers and collectors have argued this. Even today there isn't a "rulebook" that defines which charateristics of a plant should be taken into account when trying to distinguish between two plants. If there were, even within a genus, then life would be very simple and ordered. Physical characteristics are important - size, shape, tubercle orders, spine size and numbers, areoles wooly, hairy or naked, flower size and structure, etc... But also geographic distribution is important.
Taxonomy is a huge subject, and still an imprecise one. My background is in the physical sciences, so when I first started to look at this subject, I wanted to see clear rules, structures and an ordered logic to everything. But I soon came to relaise that we were dealing with a living subject, and one that has inherent variation, just as we are all homo sapiens, but that encompasses a wide variety of physical charateristics.
DNA research will be very helful, but will only, in my view, add more information on which the judgements will be made. And at the en dof the day, it is a judgement. What is a species - a subdivision, but with what rules for making the cut?

Thanks Chris.
I realize that was quite a topic. Perhaps way too broad.
I am still curious re herrarea v humboldtii - do you guys see meaningful differences - how far apart are the locations.
Well, one more correctly labelled plant re 'supertexta'. That is too bad, i have seen lots of those around this area.

There are obvious similarities between herrerae and humboldtii, but there are some differences as well - spine count (100 vs 80 radials), flower size (2.5cm wide vs 1.5cm), and location (Queretaro vs Hidalgo). They belong to the same Series, so you would expect similarities. But each species has a very limited area of distribution, so while it is possible that they share a common (and extinct) ancestor, they have developed separately, and enough it is judged by the experts to be called separate species.
As Mark (Tam on this Forum) has mentioned somewhere, the white spined plants of the Supertextae (albilanata, haageana, supertexta....) are quite closely related, and it can be quite difficult to separate them - as you saw with teh discussion on your plant.
Even really knowledgeable experts have confused species - like the confusion as to what M. lindsayi actually is - which also has featured in several threads from Hugo and Tam on the Forum. It's not easy, and amateurs like me often get it wrong.

That one to me is pretty hard - humboldtii v herrarae. I certainly agree with you re the white spined mamms not all being lumped. The seed difference may be most compelling, whatever they might be.
Spine count seems pretty questionable, tho I often do it, perhaps because it is one thing I(and other amateurs) can do. It seems like there are lots of species where the plants vary considerably in terms of spine count, lengthe, and even whether they do or don't have csp. Of course, some might say they are separte varieties or forms, but I think most wouldn't.
What I find interesting is the apparent inconsistency. I have had pretty knowledgeable folks explain how species X is so varable, flower color, csp, # of spines is all over the place. Then minutes later I ask why species Y and Z are different, and the answer is # of csp, and pink v red flower. Now maybe they are overly simplifiying, and while the varied X plants occur in one place, Y and Z are 50 miles apart.
I do realize it is line drawing, and different folks draw the lines in different places, so no clear answer.

Trying to work out the evolutionary lines of plants is difficult. Trying to judge physical characteristics is how it has been done up to fairly recently. But its not easy it seems. Just look at Astrophytums with their normal round/columnar ribbed bodies, and then at Digitostigma. Only the flower is similar to my eye at least, and of course the spotted epidermis, but body shape absolutely not!
Flower structure and seed shape and structure are important aspects, which is why you see so many SEM photographs of seeds. I remeber reading somewhere that up to 48 or so different characteristics were often assessed, including obvious external physcial ones as well as chemical and internal structural aspects.
Geographic isolation can be a fairly good measure, although recently a new plant was found in Guatemala and it turns out to be a branching form of an old plant that comes from a fairly limited distribution in the cental coastal region of the state of Veracruz in Mexico. I'm referring to Mammillaria eriacantha and the new subspecies velizii. This seems to show that there are exceptions to every indicator, but again one perhaps should not be so surprised at this, because distribution of seeds by birds is probably the most common means, and a travelling bird prsumably deposited a seed or seeds far away from where it ate them, and the seed was lucky enough to find a hospitable environment - by no means always the case. As it was, the new plant evolved enough to develop a branching habit, but not sufficiently to be different enough to allow it to be judged as a distinct species.
I had hoped that DNA analysis might help us more, but at its current stage of development, while it can show some light on family relationships but we have seen in the works published by Butterworth and by Crozier that it also shows up some rather inconsistent results. I suspect this is because the various "markers" used in the analysis are not yet sufficiently broad or understood well enough, so while they may show linkages between some plants that may not mean a 100% certainly. But they are interesting enough. For more I'd suggest taking a look at them - links can be found in the Articles section of this web site http://www.cactus-mall.com/mammsoc/index.html
Happy reading!!

Some very good points in my view. I will read that article.
Apart from DNA, we don't have much to go on re whether they evolved other than physical characteristics, do we? I suppose the parts are to guage are to what degree the plants in question have a common ancestor and diverged, or had convergent evolution, and when does teh divergence make a new species. And that is probably hard to tell w/o DNA.
Another question that I wonder about is the variation of each species. TO continue with humboldtiii, we all know all of them don't have 80 rsp. What % have 90? Same question re herrarae? Presumbaly, and hopefully, there is not much overlap - otherwise the two seem more continuous and outgh to be lumped (assuming the same is true of the other differing characteristics). And of course, one fellow might say these 3 differences warraent a differnt species, while another feolow looking at another plants with simialr differences might say it is simply a more variable single species.

Hi there

Forgive me saying it, but Haworthias!

A bit different to Mamms, but the taxonomy problems go across the board. Bruce Bayer is the man for Haworthias, and if you want to see some real angst over the concept of what makes a species, read some of his works.

We all know, secretly, that we are applying artificial man-made rules to the natural world when we try to segregate plants into species, or forms etc, but as collector's we want to know that if we are getting a plant it is going to be what we expect. As we get deeper into collecting we probably want to know more about the background and provenance of our plants, much as Chris was saying in the thread about field numbers.

How distinct species are in habitat is very questionable. New techniques for analysis of DNA etc will tell us more (and confuse us more) but it seems unlikely that we are going to find nicely defined species and genera delineated as god intended!

If you read Bradleya, Marlon Machado's article in the recent issue, discussing hybridization is food for thought. Though, as very much an amatuer, I did find it heavy going, it is worth persevering with.

Another consideration that shouldn't be overlooked is that when a new plant is introduced into cultivation, selection becomes an issue. Whilst starting off with "pure" source material, growers will inevitably choose some plants over others for ongoing breeding, and these choices will include selecting nicely spined plants, etc.

Sorry to ramble on, but I do find this fascinating!