Scientific classification
Kingdom:Plantae
(unranked):Angiosperms
(unranked):Eudicots
(unranked):Core eudicots
Order:Caryophyllales
Family:Cactaceae
Subfamily:Cactoideae
Tribe:Trichocereeae
Genus:Gymnocalycium
Species:G. pflanzii

Origin: South-east of Bolivia, North-West of Paraguay and North of Argentina (Provinces of Salta and Jujuy).

From my collection

via Flickr https://flic.kr/p/2dGiMpW