It was found in woodland at the weekend by Eric Ruaro, a long-standing hobby mushroom hunter.
It is perhaps some indication of the unusually mild weather conditions this winter that it was found, alive and well, in late November.
The mushroom season is generally late summer and early autumn.
In northern Italy, from where Mr Ruaro came originally, the mushroom-hunting season starts in August.
He pointed out the thick, firm stem, which could be sliced like a steak.
He said that normally these were maggot-eaten when found.
In fact, just under half the cap was missing, presumably already eaten by slugs (it is not just humans who enjoy a tasty mushroom).
The complete weight of the mushroom would have been over one kilo (two and a quarter pounds).
The mushroom was a member of the boleta family, he said, of which there were 45 separate members, 11 of them in Jersey (three of them poisonous).