Fucus is northern-hemisphere genus of macroscopic marine seaweeds called wracks. It includes a relatively small number of species. Fucus vesiculosus (on the picture) is perhaps the best-known species, is known to have a number of useful compounds. The plants consist of a flattened, dichotomously-branched thallus which has a small stipe and a holdfast. The blade usually has a locally-thickened area which is centrally placed called a midrib. Air bladders are Fucus vesiculosus found in some species and these help to keep the plant afloat when submerged.

This algae has traditionally been used in Eastern countries, especially in China, mainly to treat hair loss and increase desire. It has also been used as a source of calcium and iodine in places where these minerals are deficient in the human diet.