Ascophyllum nodosum is a large, common, brown alga, in the Class Phaeophyceae. It is seaweed of the northern Atlantic Ocean, also known as Norwegian Kelp, Knotted Kelp, knotted wrack or egg wrack. It is common on the north-western coast of Europe (from Svalbard to Portugal) including east Greenland and the north-eastern coast of North America.
Ascophyllum is very popular amongst the science community and has been claimed to be both the best known seaweed on the planet as well as the most researched by the academic community.
This seaweed grows quite slowly and can live for several decades; it may take approximately five years before becoming fertile.
Life history is of one diploid plant and gametes. The gametes are produced in conceptacles embedded in yellowish receptacles on short branches.
Ascophyllum nodosum is found mostly on sheltered sites on shores in the mid-littoral where it can become the dominant species in the littoral zone.
Polysiphonia lanosa (L.) Tandy is a small red alga, commonly found growing in dense tufts on Ascophyllum whose rhizoids penetrate the host. It is considered by some as parasitic.
There are free floating ecads of this species such as Ascophyllum nodosum mackaii Cotton, which is found at very sheltered locations, such as at the heads of sea lochs in Scotland and Ireland.
The species is found in a range of coastal habitats from sheltered estuaries to moderately exposed coasts, often it dominates the inter-tidal zone (although sub-tidal populations are known to exist in very clear waters). However it is rarely found on exposed shores, and if it is found the fronds are usually small and badly scratched.
It has been recorded as an accidental introduction to San Francisco, California, and eradicated as a potential invasive species there.
Ascophyllum nodosum along with Macrocystis pyferais harvested in Ireland, Scotland and Norway from which alginates are extracted it is one of the world's principal alginate supply.
Furthermore, the medicinal and dental uses have been recognized for well over a century.