I D TEASER

Could you please identify this Mammillaria at least I believe it to be a Mammillaria.I have had it for several years and it has grown and always been that colour.
https://i.servimg.com/u/f70/18/49/16/34/2013-029.jpg
https://i.servimg.com/u/f70/18/49/16/34/2013-030.jpg

Could be M. beiselii (or the beiselii-form from Arteaga), or something closely related to it. The somewhat reddish body colour might be caused by lack of water.

Wolter ten Hoeve.

I don't think that the change of colour in your plant might be caused by lack of water.
I can tell that the change of colour for too much exposure to the sun's rays or for low temperatures , is given by the action of natural substances called "xanthofille".
They are not like carotene and vitamin A precursors involved as protectors of oxidation in many biochemical processes.
Carry a part of the report on "xanthofille" by the University of Verona, diparimento of biotechnology:
The "cycle of xanthophylls", consists in deepossidazione of violaxanthin to anteraxantina and subsequently zeaxanthin. The latter is active both in the free membrane, where it contributes to the scavenging of reactive oxygen species, is bound to proteins Lhc where it induces a conformational change that increases the ability of these proteins to dissipate heat energy.
They protect the plant from the sun so violent and extreme cold.

The betaleine, which we talked about earlier, are natural pigments that are found almost exclusively in plants of the order of caryophillales where they replace the anthocyanins.
They, precursors of vitamin A, are present in the flowers and fruits of the plant, but not in the body, so it can not be responsible tanning we are talking about.
In cacti anthocyanins are not synthesized (or are only in small part) and are replaced by betalaine, in particular in the flowers.
The absence of anthocyanins and therefore of betaleine which replace them, it would be responsible for the lack of blue flowers in blue cactus.

I hope that my English can be understood.

Interesting stuff, Maurillio.

I too think that your plant is a form of M. beiselii.

Hi,Thanks for that info very interesting it cannot be the cold but it is in the direct sunlight so I will move it to a more shady position.

Attached are 2 photos of M. beiselii in habitat. Here they grow partially in the shade of larger cacti and of shrubs, but still they will get quite some sunshine. The shorter spined form is the more common one at the habitat location, the longer spined form is the exception (possibly longer spined as an adaptation to a sunny position).
My beiselii seedlings (5 months old) do have a somewhat reddish colour, they are in the greenhouse without any sun protection.

Wolter ten Hoeve.

I was given some seed which I sowed late in 2011 of what was labelled as Mammillaria beiselii f. rothii, which apparently has a different body colour to the normal species. It is supposed to be more of a grey-green colour which with some sun takes on a reddish tinge. I'm not saying that this is what your plant actually is, because I'm not sure about the naming validity, but just to suggest that there would seem to be natural variations which could be consistent enough to warrant a forma name. They seem very slow to grow and not very many germinated, so it is too early to really say much about the developing seedlings.

However, a lot has been written recently about M. beiselii, especially by Thomas Linzen who talks about it, and its various forms in his article in the 4/2012 issue of the AfM journal. In that article, he shows f. rothii and also shows photos of an old M. beiselii fa. Arteaga which has clearly reddened tubercles.