Hi, It looks most like Echinopsis lageniformis - E. peruviana is close too, but not as close. The give away traits are: groove between the ribs, round areole, wool in areole, "naked" stem surface, and a very small number of ribs. Also distinct is the curved profile of the rib between the areoles. All of these characteristics are quite stable. You can also watch for whether or not the species has a central spine emerging in the middle of the areole. This too is stable and distinctive. e.g., E. lageniformis does not have an oval shaped areole. Good luck!
