Available seasonally, fiddleheads are both foraged and commercially harvested in spring. The fiddleheads of certain ferns are eaten as a cooked leaf vegetable. They produce coiled fiddleheads that uncoil and expand into fronds. Unlike many ferns, they do not emerge as coiled fiddleheads (noncircinate vernation). The fronds spring up in clusters and emerge as fiddleheads (circinate vernation). Fossil of the croziers (or fiddleheads) of the fern fronds have been found. It is considered inadvisable to eat uncooked fiddleheads. The fiddleheads of the fern are used in floral arrangements. Pickled and frozen fiddleheads, however, can be found in some shops year-round. Coarse, reddish hairs densely cover the stipes and fiddleheads. Fiddleheads may harbour microbes, and should be washed and cooked before eating. Fiddleheads in Japan are considered "sansai", or wild vegetables. It is recommended to fully cook fiddleheads to destroy the shikimic acid. Fiddleheads contain various vitamins and minerals, as well as omega-3 and omega-6 fatty acids. Certain varieties of fiddleheads have been shown to be carcinogenic.