While the name ‘seaweed’ is a popular one, it does not in any way have value in the actual classification of these fascinating marine plants.

Seaweeds fall under the general umbrella term of ‘algae’ they are macroalgae – and normally belong to one of these three main groups: Chlorophyceae (green algae), Rhodophyceae (red algae) and Phaeophyceae (brown algae).

The overall focus on edible marine algae as a way to reduce the incidences of lifestyle-related diseases is not new.

Seaweeds have a long history of use in the east. They have been used as both food and medicine for thousands of years in China, Japan, Egypt and India.

In the sixteenth-century Chinese herbal Pen Tsae Kan Mu, algae were listed as a cure for goitre.

In sixth-century China and fourth-century Japan, seaweeds were used as folk medicines.

Stretching further back in time to ancient Egypt, the Ebers Papyrus (1500 BC) recommended using seaweeds as a remedy to treat tumours.

In the written records of China, seaweeds are even recorded as a commodity for currency and trade going back some 2,000 years.

Japan’s first written legal codex, the Taiho Code (701 AD), lists murasaki nori (purple nori) as a method of payment for annual tribute tax.

This suggests that nori was considered a high-value item. Other sources suggest that more than 30 different kinds of seaweeds were offered as payment for tax to the Japanese authorities.

Around the world, seaweeds were used in three of the major medical traditions, including Indian Ayurvedic medicine, Traditional Chinese Medicine (or TCM), and, as mentioned, in the Egyptian Ebers Papyrus.

Today, seaweeds are still referenced in the folk medicine traditions of many cultures. Although they are less well-used than terrestrial plants.

Sea lettuce is a good example. In Cuba, sea lettuces are boiled and the juice drunk to kill intestinal worms. 

While in the Pacific, they are used as a worm medicine and folk remedy for gout.

Many other species of seaweed are also widely used. Indeed, in the Pacific basin, in Hawaii and in other Polynesian islands over 29 different kinds of seaweeds are documented for their use in food, medicine and in religious ceremonies since pre-colonial times.

In New Zealand, the Māori are reported to have used seaweed meal and the milk from a seaweed-eating cow to speed up the development of a four-year-old child who was not able to sit up and talk.

In France, gathering seaweed dates back to Neolithic times. The remains of algae have been found in fireplaces during archaeological excavations. 

Seaweeds were used for heating, to fill mattresses, to feed cattle, and as famine food for humans.

Fast-forward to seventeenth-century France, seaweed ash was widely used by the glass-making industry.

“In 1692, King Louis XIV granted to Saint-Gobain’s manufacturer the privilege of gathering wreck seaweed along The Hague coast for 20 years (in Normandy). The harvesting season was fixed between the 15th of March and the 15th of September, and the ashes obtained were transported to Paris.”

Seaweeds were also burned in ovens to extract soda, particularly along the coastlines of France, which created seasonal employment for seaweed gatherers, and of course, for those people who produced and transported the soda.

By 1812, Bernard Courtois discovered iodine and its medical uses. At the time, it was dissolved in alcohol and known as tincture of iodine. 

In 1829, Francois Tissier, a chemical engineer, developed an industrial process for producing iodine. Thus, tincture of iodine came to be used extensively during wartime.

When the Second World War (1939–45) forced countries on both sides of the battle to seek alternative sources of raw materials, much attention was paid to seaweed.

These marine plants grew in abundance in the seas and oceans all around the world, and seemed to be cheap and accessible. 

An anonymous report in 1944 stated that the Germans had opened two bakeries in Norway to make seaweed bread from dried, ground and desalted algae.

A survey was also carried out along the coast of Britain to assess seaweed resources. The results of which revealed an astonishing 2,000,000 ton supply of bottomweed and rockweed. 

A later survey was carried out by the Scottish Seaweed Research Association, which revealed, in Orkney alone, 1,000,000 tons of bottomweed.

During the First World War (1914–18), a shortage of acetone led a US firm, the Hercules Powder Company of Los Angeles, to harvest and ferment kelp for the by-product of potash, from which was obtained acetone along with other products, such as iodine, alginates and common salt.

The industrial need for potash and iodine obtained from kelp declined after the war, however the kelp industry is still in operation to produce alginates.

Despite worldwide interest, a flourishing algae industry never fully developed after the First and Second World Wars. 

Where such industries exist, you might say that the harvesting of seaweeds remains on the fringe of mainstream agriculture.


  1. Chapman, VJ and Chapman, DJ. Seaweeds and their Uses. Chapman and Hall Ltd. London, New York, 1980. ISBN -13: 978-94-009-5808-1.
  2. Gomez-Gutierriez et al. Marine Edible Algae as Disease Preventers. Advances in Food and Nutrition Research. Online, 2011. DOI: 10.1016/B978-0-12-387669-0.00003-X.
  3. Xia, B. Abbot, IA. Edible seaweeds of China and their place in the Chinese diet. Economic Botany. Online, 1987. DOI: https://doi.org/10.1007/BF02859049.
  4. Fleurence, J. Levine, I. Seaweed in Health and Disease Prevention. Academic Press. ISBN: 9780128027721.
  5. Teas et al. Variability of Iodine Content in Common Commercially Available Edible Seaweeds. Thyroid. Online, 2004.
  6. Teas, J. The dietary intake of laminaria, a brown seaweed, and breast cancer prevention. Nutrition and Cancer. Online, 1982. http://dx.doi.org/10.1080/01635588209513760.
  7. Kim et al. Sea Lettuces: Culinary Uses and Nutritional Value. Advances in Food and Nutrition Research. Online, 2011. DOI: 10.1016/B978-0-12-387669-0.00005-3.
  8. Lesueur et al. Seaweed industry in France. Online, 2012. Available on Research Gate: https://www.researchgate.net/publication/278803829.

Seaweed Notebook

A Forager's Guide to the Edible Seaweeds of the British Isles

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