Fern are a common diet in Borneo and I've eaten them in long houese often.
Not great but okay.
I've been told by non- natives that older ferns can cause stomach cancer due to the irritant nature of the 'hairs'. However, proper cooking of young fiddleheads should break them down , I think.
There does not seem to be e higher than normal rate of stomach cancer amomg the natives here
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