Pleasant cactus, particularly appreciated for the extreme symmetry of the body and its thorns. It is characterized by a globose and depressed stem at the apex that tends, with growth, to become slightly cylindrical reaching about 15-18 cm in height. Its body, of an intense green tending to purple (hence the name of the species), is equipped with deep longitudinal ribs exactly symmetrical, along which protrude white woolly areolas and roundish. The radial spines are shaped like an awl, well robust and directed towards the stem, of a reddish-brownish that, when ripe, turns towards the grey; on the contrary, there is a single central spine, much longer and more massive, which turns outwards tending slightly downwards. At a certain age, when the cactus stops growing, at the apex of the plant develops a whitish spherical cephalium formed by bristles on the shades of red, from which bloom small magenta flowers with thin petals. The cephalium will then tend to grow, not in diameter but only in height, assuming a characteristic cylindrical shape that also gives an idea of the age of the plant!