Hi Mark,
I also have this RS 571, labelled as M. lasiacantha hooked spines. This plant was acquired from Wiebe Bosma,who had grown it from seed obtained from Jan Jecminek under the name JJO 4025F. After contacting Jan Jecminek, he wrote me that he had obtained these seeds from Roman Stanik. I was unsuccessful in contacting Roman Stanik.
For the moment I would label it as M. gasseriana, but I am not completely sure about this, it might turn out to be intermediate between M. gasseriana and M. magallanii.
Best wishes,
Wolter ten Hoeve, Assen, The Netherlands.