Fiddlehead

Fiddleheads or fiddlehead greens are the furled fronds from a fledgling fern, harvested for use as a vegetable. Left on the plant, each fiddlehead would unroll into a new frond . As fiddleheads are harvested early in the season, before the frond has opened and reached its full height, they are cut fairly close to the ground. Fiddleheads from brackens contain a compound associated with bracken toxicity, and thiaminase.

Source: Wikipedia