The monstrous shape of this cactus presents geometric anomalies, for example asymmetric protuberances or absence of thorns, different for each individual specimen, so much so as to make each of them absolutely unique and for this extremely sought after by collectors. In its normal form it is a very particular and elegant cactus, with a perfectly spherical shape, completely covered by long white white spines, rather thin and sometimes hooked. This clear and shiny appearance makes the cactus look like a snowball or a cotton ball, although, with its curved spines, it is anything but soft and harmless! At the beginning of spring the elegance of M. senilis is accentuated by the strong contrast that create the large, very lively red flowers, with the delicacy of the whiteness of the body.