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Subfamilia Cactoideae, tribus Trichocereae
Type species is Gymnocalycium gibbosum
The genus name is from Greek means naked calyx and refers to the flower buds bearing no hair or spines.
Distribution is in east of the Andes of southern South America, mostly in Argentina, and some grow Bolivia, Paraguay, Uruguay and Brazil.
Most species are rather small varying from 4 to 15 centimetres in size, depressed to globose stems with ribs. Flowers with naked callyxes borne from near apex, mostly white, occasionally light pink to red and yellow.
Use open soil rich for organic matter, feed with a high potassium fertilizer in summer. They are sensitive to root mealy bugs. They need full sun or light shade in hot climates. Some of them are frost tolerant.
One of the most popular South American cacti is Gymnocalycium, easily grown and producing very nice flowers. However, this has resulted over hundred of species descriptions which most of them can not be accepted. Indeed, the genus is one of the most clearly defined in the family Cactaceae.
As to The New Cactus Lexicon (2006) by International Cactaceae Systematics Group, there are 49 species and 14 subspecies in the genus Gymnocalycium. Recently Graham Charles published a magnificient book about the genus named Gymnocalycium in Habitat and Culture (2009). This very detailed reference book is mainly based on NCL classification and recognized 56 sp. and 17 ssp. in the genus. In this two books, it is accepted that the genus has 5 groups (or subgenera) according to their seed morphology :
1- Macrosemineum, 2- Gymnocalycium, 3- Microsemineum, 4- Trichosemineum, 5-Muscosemineum.
Here, I treated the Gymnocalycium names according to NCL with the aid of G.Charles' book.
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