AskDefine | Define rockweed

Dictionary Definition

rockweed n : coarse brown seaweed growing on rocks exposed at low tide

Extensive Definition

Fucus vesiculosus, known by the common name Bladder wrack, 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 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. In the 1860s, it was claimed that bladder wrack, as a thyroid stimulant, could counter obesity by increasing the metabolic rate and, since then, it has been featured in numerous weight-loss remedies.


The species is common especially 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.
Fucus vesiculosus is one of the most common algae on the shores of the British Isles. It is recorded from the Atlantic shores of Europe, the Baltic Sea, Greenland, Azores, Canary Islands and Madeira. On the Atlantic coast of North America from Ellesmere Island, Hudson Bay to North Carolina.


A common food in Japan, bladder wrack is used as an additive and flavouring in various food products in Europe. Bladder wrack is commonly found as a component of kelp tablets or powders used as nutritional supplements. It is sometimes loosely called "kelp", but that term technically refers to a different seaweed.
Primary chemical constituents of this plant include mucilage, algin, mannitol, beta-carotene, zeaxanthin, iodine, bromine, potassium, volatile oils, and many other minerals. The main use of bladder wrack (and other types of seaweed) in herbal medicine is as a source of iodine, an essential nutrient for the thyroid gland. Bladder wrack has proved most useful in the treatment of underactive thyroid glands (hypothyroidism) and goitre. }} Through the regulation of thyroid function, there is an improvement in all the associated symptoms. Though there are no scientific studies that would show a result, or lack therof; where obesity is associated with thyroid trouble, this herb may be helpful in reducing the excess weight. Though no studies have been done to confirm these kinds of claims since a healthy diet and proper exercise are the best methods of losing weight.It has a reputation in helping the relief of rheumatism and rheumatoid arthritis, both used internally and as an external application upon inflamed joints. A chemical constituent of bladder wrack called alginic acid swells upon contact with water; when taken orally, it forms a type of "seal" at the top of the stomach, and for this reason is used in several over-the-counter preparations for heartburn. The same constituent gives bladder wrack laxative properties as well. Other proposed uses of bladder wrack include treating atherosclerosis and strengthening immunity, although there is no scientific evidence at present that it works for these purposes.
Bladder wrack should not be used in cases of hyperthyroidism or cardiac problems, or during pregnancy and lactation. Excessive dosage (many times the recommended dosage) may lead to hyperthyroidism, tremor, increased pulse rate and elevated blood pressure.


External links

rockweed in Catalan: Fucus
rockweed in Czech: Chaluha bublinatá
rockweed in Danish: Blæretang
rockweed in German: Blasentang
rockweed in Estonian: Põisadru
rockweed in Spanish: Fucus vesiculosus
rockweed in French: Fucus vésiculeux
rockweed in Norwegian: Blæretang
rockweed in Polish: Morszczyn pęcherzykowaty
rockweed in Portuguese: Fucus vesiculosus
rockweed in Finnish: Rakkolevä
rockweed in Swedish: Blåstång
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