Autor: Spegazzini emend. F.Ritter

Genus superficially resembling Maihuenia.
A genus of low-growing plants forming compact cushions of indistinctly segmented stems, not easily detached, with tuberous roots (geophytic, branched plants, clumps just emerging from the ground in M. clavarioides). Stems containing a lot of mucilage. The stem segments are typically globose to egg-shaped, with tiny, deciduous leaves (polymorphic, irregular, not tuberculate, davate and cylindrical to subconical with flattened and depressed apex in M. clavarioides). Areoles situated in a depression, bearing hairs, glochids and usually spines, except at the basal areoles. When present, the spines are often flattened. In M. clavarioides, tiny, reduced areoles at the base, becoming numerous towards the top of stems, glochids absent. Spines few (max. 10), tiny, pectinate, appressed on the plant.
Flowers diurnal, self-sterile, mostly yellow, more rarely orange or red (yellow greenish to olive green in M. clavarioides), pollinated by hymenoptera. Fruits thick-walled, fleshy, indehiscent, greenish to yellowish, covered with woolly areoles bearing mostly glochids and sometimes fine spines (fruits pear-shaped, dry and irregularly dehiscent in M. clavarioides, floral remains persistent). Seeds large, flattened, pale yellow, lenticular, ellipsoid or bony, with woolly funicular enveloppe.
The genus Maihueniopsis often grows in abundant colonies in Patagonia, in very compact cushions, on clayey or sandy jlains, in the Argentine Puna on very bare areas, even in the high mountains of the Andes, between 25 m (M. darwinii) and 4850 m in altitude (M. glomerata), making it one of the genera of cacti growing at the highest altitude.
Argentina (Catamarca, Jujuy, La Rioja, Mendoza, Neuquen, Salta, San Juan, Santa Cruz), Bolivia (Potosi, Tarija), Chile (Antofagasta, Atacama, Coquimbo, Santiago, Tarapaca, Valparaiso).

Currently 20 recognised species :
– Maihueniopsis archiconoidea* F.Ritter 1980
– Maihueniopsis atacamensis* (Phil.) F.Ritter 1980
– Maihueniopsis camachoi* (Espinosa) F.Ritter 1980
– Maihueniopsis clavarioides* (Pfeiff.) E.F.Anderson 1999 (ex Puna clavarioides)
– Maihueniopsis colorea (F.Ritter) F.Ritter 1980
– Maihueniopsis conoidea* (F.Ritter ex Backeb.) F.Ritter 1980
– Maihueniopsis crassispina F.Ritter 1980
– Maihueniopsis darwinii (Henslow) F.Ritter 1980
– Maihueniopsis domeykoensis* F.Ritter 1980
– Maihueniopsis glochidiata* G.Charles 2011
– Maihueniopsis glomerata* (Haw.) R.Kiesling 1984
– Maihueniopsis grandiflora F.Ritter 1980
– Maihueniopsis hickenii* (Britton & Rose) Hunt 2011
– Maihueniopsis leoncito (Werderm.) F.Ritter 1980
– Maihueniopsis minuta* (Backeb.) R.Kiesling 1984
– Maihueniopsis molfinoi* Spegazzini 1925 (incl. M. hypogaea)
– Maihueniopsis ovata* (Pfeiff.) F.Ritter 1980 (= T. russellii)
– Maihueniopsis platyacantha* (Pfeiff.) D R.Hunt 2011
– Maihueniopsis reicheana (Espinosa) Kattermann & Lode 2014
– Maihueniopsis wagenknechtii F.Ritter 1980

References: "TAXONOMY of the CACTACEAE" -  ISBN 978-84-617-3692-8 (Vol. 2)