Sometimes it is more important to say what a Dyckia is not than what it really is. This is the case here.

A mysterious pretty one Dyckia sp.

Not a Dyckia distachya,
Not a Dyckia sthreliana,

Not a Dyckia sthrelloa,
This is a reophytic fro Rio Grande do Sul, this is all I can say.
Many mistakes have been committed with this beauty here.
This plant was collected by a bush man who understands nothing on Dyckias.