The name macracanthus derives from ancient Latin and means " large thorns". The stem of Melocactus macracanthus has well-marked longitudinal ribs and a globular shape that tends to lose with growth, rising upwards. Upon reaching adulthood, small pink or purple flowers sprout above the cephalium, which in turn will continue to grow steadily over the years. Above it also sprout small pink fruits, with the shape similar to an egg. Along the ribs, straight, strong reddish spines grow which can reach up to 3 cm in length.