In its natural habitat, high in the mountains, it often grows on rocky slopes in the shade.

It is grown as an ornamental plant, appreciated for its dense spines and pink flowers, which are especially large in the subsp.

ascensionis had been described as a separate species by Werner Reppenhagen in 1997, but quickly reduced to a variety by Foster and Glass.

[3] A 2004 study shows that Mammillaria glassii forms a clade with M. carmenae, M. pectinifera, M. picta, M. plumosa, and M.

The body is entirely concealed by a dense covering of spines and bristly white axillary hairs.

[3] Fruits are edible;[6] they start green and turn pinkish as they mature, containing black seeds.

glassii by its larger stems, measuring 2 to 10 cm in diameter, fewer axillary hairs, a more rounded top, slightly woolly areoles, and longer central spines.

Most notably, it features much larger flowers, measuring 18 to 22 mm wide and ranging in color from pale shell-pink (seen in the former var.

glassii has been recorded in the Mexican states of Coahuila, Nuevo León, and Tamaulipas at elevations of 1,450 to 2,250 meters.

ascensionis is found at 2,400 to 2,750m altitude in Nuevo León, growing in moss and limestone as well as in crevices on steep cliffs, where it receives sunlight only in the late afternoon.