Gymnocalycium is a genus of about 70 South American species of cactus. Their main area of distribution is Argentina, part of Uruguay, Paraguay, southern Bolivia and part of Brazil. Most species are rather small varying from 4 to 15 centimetres in size. They are popular for their easy flowering habits, although the flowers are generally brightly coloured. They are also popular for their ease to care for. The genus name "Gymnocalycium" comes from the Greek for "naked calyx" referring to the flower buds bearing no hair or spines.