Fucus vesiculosus, known by the common name bladderwrack, is a seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans, also known by the common names black tang, rockweed, bladder fucus, sea oak, black tany, cut weed, dyers fucus, red fucus, and rock wrack.
It was the original source of iodine, discovered in 1811, and was used extensively to treat goitre, a swelling of the thyroid gland related to iodine deficiency.
The species is especially common on sheltered shores from the middle littoral to lower intertidal levels. It is rare on exposed shores where any specimens may be short, stunted and without the air vesicles.
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