Most southerly cactus species

The most southerly growing cactus is likely to be a species of Austrocactus native to the southern end of South America in Chile and Argentina. For example, A. aonikenkensis, first described in CactusWorld in June 2018, is endemic to the Patagonian province of Santa Cruz, Argentina, with a range extending to at least 50.86°S, and perhaps as far as the city of Río Gallegos (51.6°S).

A. aonikenkensis was first formally described by hobby botanists Elisabeth and Norbert Sarnes from Germany in Vol. 36 of the journal CactusWorld, published by the British Cactus and Succulent Society. Its binomial was chosen in acknowledgement of the indigenous Aónikenk (aka Tehuelche) people also native to Argentina's Santa Cruz province.

A close contender for the most southerly cactus is Pterocactus australis, with a range at least as far south as El Calafete, Argentina, at a latitude c. 50.3°S.

The most northerly growing species of cactus, meanwhile, is the pygmy or brittle pricklypear (Opuntia fragilis) with a range extending as far north as 56.28°N, in the vicinity of the Peace River Valley in Alberta and British Columbia, Canada.