Mammillaria goodridgei rectispina

This little plant doesn't increase in size much, but it has flowered for the last couple of years. I bought it as a seedling 3 years ago and it is still in a 7cm pot.

Dear Chris, just thought you might want to see its mother and what it could look like in about 25 years.

Wow!!!!
Not much else to say - your plant?

I wish. This belongs to Len Evens from Coventry. I visited him when I was down for the AGM. He used to do a lot of showing years ago. This is a habiatat plant which came from the T.L. Over the years Len has grown loads of seedlings and sold them on to Nurseryman including John Henshaw. This plant has produced BOTH straight spined AND hooked spined plants.

Interesting, which would suggest that there is only one species, and rectispina is merely a descriptive add-on, not even a forma. Or, of course, that the plant shown isn't a true species but a hybrid. Now if there were a goodridgei and a rectispina that do interbreed, that could be the answer.
I wonder which is true? I suspect that we'll never know.

I would not recogize rectispina has anything. I do not belive plants having straight spines or hooked spines is has fixed a genetic characteristic has we tend to think. There are many species that will have both straight and hooked spines plants, an example being your M.capensis var pallida. Then there are species who DON'T usually produce any central spines but sometimes will, i.e members of the lasiacantha. And then you will get species that usually DO produce central spines but some time don't i.e M.haageana ssp conspicua in its form albidula.
There is no need to speculate on M.goodridgei / rectispina interbreeding has from what I have been told the species is how extinct in habitat. So look after the ones you have, that is if you accpet goodridgei has a good species and not a sub-speices or island form of M.dioica.

Yes, I know the stories about the fact that it is extinct. I wonder though how many people have been to all the various islands in the Isla de Cedros and Guadalupe region?
I agree with you that there are a number of plants that we know as good species that have forms with straight spines and forms with hooked spines. As well as capensis, there is albicans, marcosii, rekoi, just to cover a few Series! We also know that the genetic profile of plants can produce varied forms from a single plant. They seem to contain a strong propensity to evolve. I've even seen a red flowered dioica.
However, another reason could be that two close species have interbred, and given rise to a very variable mix of plants. Sometimes the original parents might well have died out, and so what we see as a result is a variable species. Or perhaps they do still exist, in the same locality and then what we see gets even more complicated. As far as goodridgei, I have read (but can't locate the reference at the moment, unfortunately) that the straight spined form grows mainly on one side of the Isla de Cedros, and the hooked spine on the other, with mixed populations in between. Now that could just be geography favouring one form, or it could be something else.
What I'm really saying is just don't rule out some of the other possibilities - botany is an approximate science, and judgements are made often without as much data as the botanists might like. As one who trained as a physical scientist, I would love clear rules, that x follows because of y, but the plant world isn't like this. Sadly!