Acting on a hunch…

…I did a little exploratory Surgery.  My hunch was correct.  They propagate in a somewhat spud-like manner.  Each tuber has set out to become a new plant.
They were so shrouded by the Ocas last year I could barely see them, and, by the time the Ocas had reached harvest i.e. Tops well frosted, I saw no sign of the Chinese artichoke (Stachys affinis).
Chinese they are, Artichokes they ain't. 
Who'd have thought they were related to the "Lamb's lugs".  (Stachys lanata) 
So, upon the morrow they'll be replanted "at stations" and kept away from the more rampant Oca to see what crop emerges.
Well! All bar the one I've just nibbled anyway.
;¬)
B T W there's  another clump, untouched, plus what's left of this clump.