A very big group of very special plants from South America. Usually shaped in the form of a flattened sphere, with not too many spines, green epidermis and big mostly white flowers. Very popular amongst hobbyists some of whom collect exclusively Gymnos (a nick-name). There are between 70 and 120 species, depending on recent fashion. They are very easy! The potting mix may contain some soil and should be slightly acidic. No need for the full sun, no need for light in winter (temperature 5–12°C), no problem if overwatered, no problem if kept dry for a long time. And you get a carpet of flowers for months. It is a must!