Mammillaria schwarzii comes from central Mexiacn state Guanajuato from altitudes above 2000m. In culture plants form multi-headed mounds, with small but plentiful white or pale yellow flowers. It is a modest but beautiful plant.
Mammillaria schwarzii is reported in literature as a somewhat difficult plant, a claim that I can not confirm. In my culture it gets no special treatment. Plants do well at full sun, in a cooler location in the greenhouse next to the vent.