Fucus serratus is a seaweed of the north Atlantic Ocean, known as toothed wrack or serrated wrack. It is olive–brown in colour and similar to Fucus vesiculosus and Fucus spiralis. It grows from a discoid holdfast. The fronds are flat, about 2 cm wide, bifurcating, and up to 1 m long including a short stipe. It branches irregularly dichotomously. The flattened blade has a distinct midrib and is readily distinguished from related taxa by the serrated edge of the fronds. It does not have air vesicles, such as are found in F. vesiculosus, nor is it spirally twisted like F. spiralis.
The reproductive bodies form in conceptacles sunken in receptacles towards the tips on the branches. In these conceptacles oogonia and antheridia are produced and after meiosis the oogonia and antheridia are released. Fertilisation follows and the zygote develops, settles and grows directly into the diploid sporophyte plant.
Distribution and ecology
Fucus serratus is found along the Atlantic coast of Europe from Svalbard to Portugal, in the Canary Islands and on the shores of north-east America.  It was introduced to Iceland and the Faroes by humans within the last 1000 years where it was first noted in a phycological survey in 1900. It grows very well on slow draining shores where it may occupy up to a third of the area of the entire seashore.  It often dominates the rocky parts of the lower shore, exposed or immersed in rock pools, on all but the most exposed shores.  “…the littoral zone is characterized especially by such phaeophyta (brown algae) as Ascophyllum, Egregia, Fucus and Laminaria, particularly when the shore is rocky."
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