IN THE EARLY days of cactus taxonomy few cacti were yet discovered, precious little was known about them, and there were just a few described genera in which to place any newly discovered species. Thus many species were at first placed in the genus Echinocactus established by Link & Otto in 1827. (Link & Otto, 1827, Echinocactus, Negotiations of the Association for promotion of Horticulture in the Royal Prussian States, Volume 3: 420-432). As more plants were discovered and more was learned about them, here and there species were gathered into groups. Sometimes the taxonomists proceeded with caution and created subgenera within Echinocactus. Eventually, these subgenera were given status as genera in their own right. This was the path for Notocactus, made a subgenus in 1898 by Karl Moritz Schumann, (Karl Moritz Schumann, 1898, Gesamtbeschreibung der Kakteen, p.379) then raised to genus by Alberto Vojtěch Frič in 1928. (Tony Mace, 1975, Notocactus) By recent taxonomic treatment, the notocacti are to be placed in the genus Parodia. However, you will find many nurseries still recognize Notocactus, which in fact will save you a good bit of trouble. For truth be told, the notocacti are almost embarrassingly easy to grow whereas the other species of Parodia are difficult at best, even in a greenhouse.