Echinopsis oxygona is native to Uruguay, South Brazil and Argentina, however as many other cactus plants, they can be grow at home too.
There are many different sizes from 3 inches to 12 inches tall and 10 inches in diameter, but to reach these number you need to know how to take care of them.
As many other cactus plants, they need water, but they also like a longer drying term between waterings. From my personal experience, in summer they like to be in a sunny hot place, with 1 watering a weak. However in winter I recommend you to take them in a cool place but never outside. They can't really survive the temperature below - 10°C, so make sure that they are in a warmer place. Although the like summers and hot weather, it is important for them to have a relaxing term, usually in wither. Put them in a cool place, maybe a garage or a hut for at least 2 months, so they can relax and save energy for the growing term in summer.
Furthermore, never let them sit in a pool of water, they don't need much so too much might result them dying.
If you take care of them well they may grow flowers and fruits like mine did.
Here is how this species look like:
I hope my post was helpful, please upvote is you liked it.
Thank you, have a nice day.