Dyckia or Deuterochondia sp. Bolivia
A plant native to dry Chaco where it can be found with skinny stemmed tree cacti; leafless Mesquites, that have 8" thorns; Gymnocalycium pflanzii: several Echinopsis and enough other spiny things to seriously pluck the scales off of a dragon's tail.
This plant develops 8" to 10" diameter rosettes and with time spreads and make sizable colonies. The acid green leaves have an even row of teeth lining the leaf margins which resurvey toward the center of the plant and are sharp enough to grab and take hold. Cold hardiness is unknown, we are only guessing that it is hardy to Zone 9.
We are also guessing that it is a Dyckia. It might well be a Deuterochondia species. Both genera occur at the site of the collection and the person that sent us the seed admitted they could have collected the seed from either plant. Currently the resulting seedling are starting to look a bit like a Deuterochondia. We will only know what it is for sure once it blooms. Dyckias develop a flower spike off to the side of the main rosette while the Deuterochondias in the area produce a terminal flower spike out of the center of the main rosette.

