Pot: 10 cm.
The name of the species was chosen in honor of the famous cacti collector Charles E. Glass. It is a small, globular cactus, which does not exceed 10 cm in diameter, that tends with age to form large tufts consisting of groups of numerous heads, often all of similar size. It has cylindrical sapless tubercles, completely hidden by thorns which constitute the true peculiarity of this cactacea and make it so appreciated. They are white radial spines similar to hair, soft, very thin and dense, which cover the whole plant. The soft appearance due to the fluff contrasts with the single central spine that protrudes from each areola and is instead strong and hooked, but so small that it often disappears in the middle of the "hair". The whiteness dwindles in the beginning of spring, when a wonderful corolla of small flowers blooms, pink sometimes in shades of yellow in color.