Fiddlehead Ferns are a type of green vegetable, specifically "the furled fronds of a young fern, harvested for use as a vegetable. Left on the plant, each fiddlehead would unroll into a new frond," (Source: Wikipedia). Some cooking blogs and chefs suggest that fiddleheads can be cooked similarly to how you might prepare asparagus (for safety reasons, most experts advise NOT to eat these raw, including farmers' market-purchased fiddleheads and especially anything foraged from the wild forest). They are a good source of Vitamin A and C.
These pictures comes from Far West Fungi, a family-run, certified-organic "cultivator of edible/medicinal mushrooms, & wild forest products," with consumer presences in the SF ferry building & farmer's markets." See more about Far West Fungi via the links below.