N.B. Information on many more species can be found under the sections dealing with the history of seaweed use and their applications in medicine, fertiliser, food and recipes, etc.

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Ulva lactuca

This is one of the green seaweeds.  The 'true' sea lettuce - Ulva lactuca - is a very rich source of iron and has been eaten in Scotland for many hundreds of years.  This species may be eaten raw as a salad vegetable, or else used in soups.  A closely related species, Enteromorpha intestinalis, is also used in cooking and is excellent when deep-fried to a crispy consistency.

Ulva lactuca is the Scottish species with the consistently highest vitamin C content, although many other species contain levels which fluctuate widely over the course of the year.  A polysaccharide compound, isolated in 1994 from sea lettuce, has been shown to have considerable antiviral effects, reducing replication rates of a number of strains of human and avian influenza viruses.
 

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Laminaria digitata

This large and sturdy brown seaweed is one of the most common of the 'kelps'.  Extensive 'forests' of this species, usually partly exposed at low tide, are found around the coast of Scotland.  These kelp forests provide a highly diverse habitat for many crustaceans, molluscs, fish, seals and other seaweeds. 

Laminaria digitata is recorded by Martin Martin (18th Century) as being used to induce appetite in a young man who would not eat.  The leaf-blade was boiled and the resulting water drunk with a little butter.

The ability for seaweeds to absorb large amounts of fluids when rehydrated has meant that they have been put to use in order to hold open wounds. Portions of the stipes of Laminaria species can be placed crosswise in a wound and by absorbing blood (and thereby gaining rigidity) they can hold the wound open. Such techniques are also used in gynæcology to dilate the cervix.

The stems of Laminaria digitata were once used to make knife handles.  When the stem hardened (around the shaft of the knife handle) it was said to be as durable as and similar in appearance to stag's horn. 

This species is used as a vegetable and can be eaten along with dulse or boiled and served with butter, pepper and vinegar.  In some areas it was a favourite of children who roasted the stipes and spread the resultant paste on bannocks.

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Laminaria saccharina

Laminaria saccharina is the sweetest of Scotland's native seaweeds and is said to have a taste reminiscent of peanuts. The Reverend Landsborough (1849), however, suggests that it is not as palatable as others might think: "it is not relished as food; indeed the Norwegians we are told esteem it so lightly that they call it Toll-tare, implying that it is fit food for the Fiend". 

'Toll-tare' actually refers to the fact that sugar-wrack is a typical seaweed found at the border between land and sea (Toll = boundary / border, Tare = kelp). How the devout Reverend Landsborough made the connection between this name and satan is beyond this writer. Perhaps he confused it with Trolls.

In the 19th Century L. saccharina was sold in the streets of Edinburgh, as a snack, along with a number of other seaweed species, advertised by the cry of "Wha'll buy dulse and tang?"
 
 
 

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Fucus vesiculosus

The wracks are some of the most abundant of the seaweeds on our shorelines.  They are widely harvested for use as fertilisers, in the 'lazy beds' of the crofters, and are also employed in the cosmetic industry.

On Jura, an infusion of Fucus vesiculosus (sea-ware) and another plant called 'red fog' (probably one of the grasses Holcus lanatus or Festuca rubra) used to be inhaled to treat distemper.  Tinctures and tablets of F. vesiculosus are available from health food shops. They are typically used for their iodine content as a dietary supplement.  Seaweeds (both raw and as supplements) are the principal source of this essential element in the diets of vegans.

The belief that iodine 'stimulates the thyroid', and thus accelerates the metabolism, has been used to suggest that seaweeds may be useful as aids to slimming.  A number of different preparations making use of this property have been marketed over the last century and a half, although there has been considerable scepticism from the scientific community.
 
 
 

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Ascophyllum nodosum

The knotted wrack, Ascophyllum nodosum is by far and away the most commercially significant species for fertiliser production. Dried and milled Ascophyllum meal is processed by companies in a procedure called composting (essentially replicating the effects of the natural breakdown process). The meal is heated under pressure (like a pressure cooker) and this lyses (breaks down) the cells, releasing the nutrients. Additives such as preservatives may be included in the final mixture. 

Seaweed meal for livestock such as cattle and sheep is one of the major uses of seaweed in Scotland (second only to their uses in alginate and fertiliser production). For the production of meal, it is generally fresh cut Ascophyllum nodosum which is used, as cast weed is very nutrient poor. 
 
 
 
 

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Palmaria palmata

Dulse (Palmaria palmata) has been put to many different uses in Scotland.  This includes using an extract as a brown dye for textiles. Dulse has also been put to a wide variety of medicinal uses.  As well as a cold compress and wound dressing, this species also:

• Acts as an emetic and cure for worms when taken dried, after fasting.  A number of other species are used by cultures throughout the world as vermifuges.
• When taken as a soup (càl duilisg in gaelic), dulse served to treat constipation and stomach complaints in general, as well as maladies of the skin. 
• The Reverend Landsborough, writing in 1849, records that dulse "was thought very efficacious as a sweetener of the blood, and in warding off, or curing, scorbutic and glandular affections."  This may refer to the fact that the high iodine content of dulse (and seaweeds in general) is useful in combating thyroid gland (gaelic: brisgein) problems.
• In some parts of the Highlands dulse soup was a favourite up until the late 1960s and would be eaten several times a week if used as a treatment.
• In the islands, raw dulse was chewed in order to alleviate hunger during work, as well as to improve eyesight.
• In 18th Century Skye, the lamina ('leaf blades') of dulse were boiled with a little butter and then used as a compress to induce sweating in fever patients. 

Dulse is a very tough seaweed and was typically chewed raw, or boiled (for up to five hours!) and used as an appetiser.  This plant can also be roasted, stir-fried or dried.  On Skye it was boiled and served with butter as a separate dish. 

  Cullen skink with dulse

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Porphyra umbilicalis

Sloke was traditionally pounded and stewed with butter or other fat to produce a jelly - like substance.  This was often flavoured with leeks or onions and was purported (by Martin Martin 1703) to be the only food that a human might need to survive. This sloke jelly was eaten with oatcakes by fishermen from Caithness. An alternative is to take the jelly and add it to oatmeal to give flat bannocks (or laverbread in Wales).
 
 
 
 
 
 
 

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Chondrus crispus

Chondrus crispus or 'Irish moss', with its jelly-like consistency when boiled, has been put to use as a nourishing food for invalids on a 'no-solids' diet.  It has similar properties to dulse in its ability to settle an irritated digestive system and was used for similar purposes. More recently, this species has been used as an anti–coagulant and as a soothing treatment for stomach ulcers.

The jelly is delicate (some say bland) in flavour and can be used as a thickening agent in soups and stews. If reduced to jelly in milk a sort of blancmange (called karrikin on Skye) is formed, which needs lemon, vinegar or other flavour added.

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