Mammillaria sempervivi ?

It's wintertime. Time for me to identify some plants from former trips to Mexico.

This one we found between Tepeji and Tula, Hidalgo. Leucocephalae or Macrothelae.. I'm really unshure. M.sempervivi may be a suggestion. Other ideas?

Hi Robby,

This plant looks quite similar to some plants that I found near Venados, Hidalgo in 2005, which were clearly M. sempervivi with yellow flowers. The 4 spines are a bit longer than on the plants I found, but the white wool is very similar.

This is what it looked like:

Thank you Chris! A very beautiful plant you show us here. You were lucky to see them in bloom.

Yes I agree both plants are the same species. Even if my plant have no flowers M.sempervivi fits best.

My vote goes to M. pseudocrucigera.

Wolter.

If only Robby's plant had flowers, then it would be clear. I do have reservations about the longer spines, so wouldn't rule pseudocrucigera out. These two have been confused by many over the years.

CRAIG wrote in his Mammillaria Handbook about M.sempervivi var. tetracantha (DeCandolle) and he showed a picture of this plant. This fits our find very well.
He spoke about various places where they collected this form, not far from our habitat. Maybe this is the missing link. Today M.sempervivi var. tetracantha belongs to M.pseudocrucigera.
Without flowers there won't be a better choice. Thanks to chris and wolter for discussing this species!