conserved Mammillaria. Mammillaria is a large and diverse genus with many species often exhibiting variations due to the nature of terrain, weather, soil and other ecological factors. As a result, subdivisions within the species has been rather inconsistent over time. Initially, some investigators were more inclined to consider each variation as a unique species, although as time went on, creating confusion and long synonymy-lists for some of the species. Over time, new investigators began grouping closely related forms under the same name to attempt to more accurately define the species. Several systems for classification began to emerge. The first of note, created by Schumann and modified by Berger, divided the species into ten named groups. However, the criteria for these divisions was somewhat indefinite and flexible. In the early 1923, cactologists Nathaniel Lord Britton and Joseph Nelson Rose developed the Britton & Rose system which arranged the classification characteristics in a system of keys with tangible separation factors, resulting in a much more workable system of identification. Later classification was performed by the cactus specialists Hunt, Reppenhagen and Luthy, with much work focusing on researching the meanings and value of the original plant descriptions, synchronizing them with modern taxonomic requirements and studying the morphology of plants and seeds, as well as ecological aspects of the genus. These works helped to expand the understanding of Mammillaria taxa. Currently the classification of Mammillaria is in a state where few newly discovered species are likely, though some new species may yet be found when the chaos of names created earlier by commercial plant collectors is sorted out. Many names that were introduced for plants barely differentiated by a shade of flower colour or variation in spination were eliminated in attempt to make the use of names consistent with the rest of the botanical world. The number of taxa, which at one time numbered above 500, is now below 200. Some genera (Dolichothele, Mammillopsis, Krainzia and others) have been merged back into Mammillaria, and others like Coryphantha, Escobaria and Mammilloydia were confirmed as separate. Intense studies of DNA of the genus are being conducted, with preliminary results published for over a hundred taxa, and this promising approach might soon end the arguments. Based on DNA research results, the genus does not seem to be monophyletic and is likely to be split into two large genera, one of them possibly including certain species of other