The Gunnera is not related to the rhubarb ... quite a distinct species
I certainly wouldn't like to try a Gunnera pie and custard
Ireland is warmed a little during the winter by the warm Gulf Stream. temperatures might get down occasionally to around minus 12 Centigrade (unsure what that is in Faranheit) The coldest I remember is about minus 15C
That would be Zone 8 for us here in the States, but with much different summers, at least than our Southeast zone 8! Maybe similar to the Pacific Northwest coastline. I saw a gardening show a few years back, maybe Victory Garden on PBS, that gave a tour of a garden in Ireland that grew many tropical plants year-round, it may have been Vandeleur. Does that sound right?
Steve