The crested form Mammillaria duwei f. monstrous is a very peculiar cultivar for its shapes and colors, and for these characteristics it is highly sought after by collectors. Its stem is completely wrapped in a thick white-yellowish down giving it an almost velvety effect. In the midst of this perfection, single yellow central spines emerge, hooked, which however are not present in all specimens. Its irregular and monstrous shapes give it a unique and unusual appearance.