Rebutia jujuyiana

Purchased at a C/S society sale, labeled R. jujuyiana.  The only online reference I could find on this named plant is a listing of Rebutia species in a 1976 publication of 
Ashingtonia; Vol 2, No. 7.  The colors are very true in this photo.  I will continue to investigate the accuracy of this name.  For now, I consider myself just lucky to have 
such a beautiful plant!

Rebutia krainziana

Rebutia heliosa condorensis

No water in winter.  Infrequent water in summer (growing season).

Rebutia arenacaea

The plants should be kept almost completely dry during the winter months, only water them to prevent the roots from completely drying out, once a month should be fine. From March onwards the plant will begin to grow and watering should be increased gradually until late May when the plant should be in full growth. 

During hot weather you may need to water the plants once a day so long as the plant is actively growing.
From late September watering should be reduced to force the plant to go in to a state of semi dormancy, by November you should be back in to the winter watering regime (dry).