Another unknown in habitat

Another mystery Mamm that needs identification. This was found about 3.6 km NW of Santo Domingo, San Luis Potosi. The same highway that goes towards Huizache.

https://i.servimg.com/u/f22/13/02/58/84/dscf4510.jpg

I have croped a close up of the Mamm.

https://i.servimg.com/u/f22/13/02/58/84/mamm_s10.jpg

Reppenhagen reports M. leucocentra from the Santo Domingo area (Rep 1049). I think that he misidentified these plants as M. leucocentra, because M. leucocentra grows near Zimapan, in the wonderful Barranca de Tolimán.
From the Huizache - Cerritos region he reports M. brauneana (Rep 1003, 1008a, 1074, 1440). I have my doubts about several of these identifications.
In my opinion, your plant is M. albata or perhaps a transitional form to M. formosa. Not so far away, north of Presa de Guadelupe, I found plants which I have assigned M. albata status (WTH 576), with a small question mark, however. Some plants really looked like M. albata, others were much less woolly and looked somewhat like M. formosa. The attached photos show the differences between the plants from the same location. I hope that this also makes clear that attaching a name to an unlabelled plant (as is the case in nature) is very difficult.

Wolter.

These are the M. albata found in the same locality. They are very different from the "mystery" plant I have shown. I always like to put a name to plants I find, perhaps that one was a one off.

https://i.servimg.com/u/f22/13/02/58/84/dscf4512.jpg

https://i.servimg.com/u/f22/13/02/58/84/dscf4513.jpg

https://i.servimg.com/u/f22/13/02/58/84/dscf4514.jpg

OK, you won, your first plants are not M. albata. But what then? A form of M. brauneana, M. formosa, or M. idontknowii?

Wolter.

I do not know Wolter, that is why I posted the picture in the first place. It is not a matter of winning just that we learn from each other and there is always someone somewhere who might give it a name. Thanks and cheers.

I always like habitat identification attempts, as it is so dificult with the variability of wild plants. I can't give you an identification, but just some thoughts.......

I think your plants look like M. chionocephala without the wool and bristles! Since M. ritteriana is thought by some to be a M. chionocephala with lots of wool, perhaps there is also a form without?

The spine counts seem to be about right for this species, as do the tubercle shape, just lacking in those two important characteristics of bristles and wool.

I see from Pilbeam that it isn't formally acknowledge from SLP, but he does comment that it has been reported from Huizache, Charco Blanco and Guadalcazar, though he thinks they are mis-reports of M. formosa. Is it possible that they are not?

I will stick with albata even though Pilbeam does not recognise it. I think chioocephala is different in that it has larger heads (except ritteriana) and grows further North. From what I have seen there is a gradual whole complex from, South to North, from leucocentra ,albata, formosa and its subspecies microthele to brauniana, ritteriana/chionocephala and also I might add klissingiana.

But what is your opinion of the first photo, Chris?