Phycologists consider seaweed to refer any of a large number of marine benthic algae that are multicellular, macrothallic (large-bodied), and thus differentiated from most algae that tend towards microscopic size (Smith, 1944). Seaweeds are found among the green, red, and brown algae. Some cyanobacteria may also be counted as seaweeds. Seaweeds are named after terrestrial "weeds", and are not to be confused with things like seagrass which are vascular plants and not algae.

Table of contents
1 Structure
2 Uses
3 References


Seaweeds may have an appearance that resembles a non-arboreal terrestrial plants.

  • frond or thallus: the algal body
    • blade: a flattened structure that is somewhat leaf-like
      • sorus: spore cluster
      • on Fucus -- Air bladders: float-assist device (on blade)
      • on kelp -- floats: float-assist device (in between blade and stipe)
    • stipe: a stem-like structure
    • holdfast: specialized basal structure providing attachment to the bottom


Seaweeds are used extensively as food by coastal peoples, most particularly in Japan but also in Korea, in Peru and in the Canadian Maritimes. For example, nori is a dried red alga, formed into sheets, and used to wrap sushi. Irish moss is another red alga used in producing various food additives. Other seaweeds may be used as seaweed fertiliser.


  • Smith, G.M. 1944. Marine Algae of the Monterey Peninsula, California. Stanford Univ., 2nd Edition.

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