According to Wikipedia, the stems of Gunnera tinctoria are edible
http://en.wikipedia.org/wiki/Gunnera_tinctoria
but it is also an invasive species that is causing problems crowding out native vegetation in New Zealand and Ireland. No comment on the edibility or otherwise of the many other species of Gunnera.

definitely not poisonous: bit prickly when you brush past it. Mine has been mistaken for giant hogweed (which is unpleasant).