Source, Etc

Bladderwrack, Fucus vesiculosus, Linne (Class, Algoe,; Subclass, Phoeophyceoe; Order, Fucacea3), is a seaweed widely distributed on the shores of the Atlantic Ocean, and one of the commonest seaweeds on the coast of Great Britain, growing on the rocks and stones exposed at low tide. For medicinal use, the entire living plant should be collected and dried. That which is thrown up by the sea should be rejected, as by contact with the sea water it is liable to lose some of its constituents, which easily diffuse out from those cells the protoplasm of which has lost its vitality.


Bladderwrack, when fresh, is of a dark olive brown colour, changing, as the weed dries, to nearly black. The thallus of the plant is thin and flattened, about 2 cm. wide and up to a metre or more long. It has an entire margin, and branches dichotomously, bearing at intervals bladder-like swellings (air-vesicles) arranged mostly in pairs; some of the branches terminate in club-like enlargements, in which the organs of reproduction are situated. When slightly moist it is cartilaginous, but when quite dry, hard and brittle. It has a peculiar seaweedy odour and a disagreeable, mawkish, mucilaginous, and saline taste.

The student should observe

(a) The entire margin,

(b) The vesicles usually in pairs.


Bladderwrack yields to alkaline solutions a gelatinelike substance found in other seaweeds and termed algin. The plant yields by hydrolysis mannitol, fucose and arabinose.

It also contains mannite and a small proportion of iodine. The latter appears to exist in the form of an organic compound (Eschle, 1897), similar in its nature to the iodine compound found in thyroid glands. This is probably the most important medicinal constituent of the drug.

The dry plant yields about 0.0113 per cent. of iodine (v. Itallie, 1889), and 1.6 to 3.0 per cent. of ash, in which chlorides and bromides are present in addition to iodides.

Algin is prepared commercially by macerating seaweed in water and boiling the insoluble residue in a solution of sodium carbonate; the algin (or alginic acid) dissolves and is precipitated from the filtered solution by hydrochloric acid; the precipitate is redissolved in soda and the solution evaporated on glass plates; it is used as a calico dressing and for thickening the colours used in calico printing.


Preparations of bladder-wrack have been used medicinally to reduce obesity.

Varieties, Etc

Fucus serratus, Linne, also a common seaweed occurring with F. vesiculosus on the rocky shores of Great Britain, has a serrated margin and no air-vesicles, whilst F. nodosus, Linne, has the vesicles usually single, not in pairs. The constituents of these seaweeds are probably similar to those of F. vesiculosus.

Fig. 113.   Bladderwrack. Branch with reproductive organs. Natural size. (Maisch.)

Fig. 113. - Bladderwrack. Branch with reproductive organs. Natural size. (Maisch).