It is not a moss, it does not grow only in Iceland, and in times of hardship it was baked into bread: Iceland moss (Cetraria islandica) is a lichen, a partnership of fungus and alga, and has accompanied European plant lore for centuries. Here is everything worth knowing about this brittle, bitter and surprisingly tough lichen, from its appearance and history to preparing it as a tea.
Why this lichen is not a moss and still carries the name
Lichens are not plants in the strict sense. A fungus and an alga, sometimes also cyanobacteria, together form a body that botany calls a thallus. The fungus provides support and structure, the alga energy from light. Iceland moss is not related to a true moss.
Iceland moss belongs to the Parmeliaceae family and is easy to recognise. The thallus grows up to about 15 cm long and consists of irregularly forked, channelled or almost flat, stiff bands 0.3 to 1.5 cm wide. The upper surface is greenish to brown, the underside greyish-white to light brownish with pale, sunken spots known as respiratory cavities. The margin often looks slightly fringed. Brown, disc-shaped fruiting bodies on the tips are very rare. Dry, the lichen is brittle and crisp; in water it softens and swells.
Where Iceland moss grows and where it comes from commercially
The name is misleading, because the lichen does not grow only in Iceland. It occurs in Arctic and subarctic regions, in northern and eastern Europe, Siberia and North America, and also climbs into middle and high mountain ranges, for example in Germany, northern Italy, the Czech Republic, Slovakia and Poland. It grows loosely on the ground.
According to the assessment report of the European Medicines Agency (EMA), the material for commercial use comes mainly from northern, central and eastern Europe, especially Scandinavia, Bulgaria, the countries of the former Yugoslavia, Romania and Canada. Because lichens take up substances directly from the air, origin is not a minor matter (more in the safety section).
From emergency food to tea herb: a lichen with a long history
Iceland moss has appeared in books since the Middle Ages. The botanist Valerius Cordus mentioned it early, and in 1672 Bartholin described the lichen under the name "Lichen islandicus". Linnaeus considered it an important plant in 1737. In 1813 the chemist Berzelius isolated from it the first polysaccharide fraction ever obtained from a lichen. It has its place in Switzerland too: the Pharmacopoea Helvetica listed it in 1953, 1971 and 1987, besides the German and European pharmacopoeias.
In the north the lichen was above all food. In Arctic and subarctic areas it served as emergency food in years of famine and was also made into bread and sweet dishes such as jelly in normal years. The problem was the bitter substances, so the lichen was treated with wood ash and boiling water. Feeding experiments show that untreated material is tolerated less well than pre-treated material.
What is in the lichen: a quarter to a half is mucilage
Most of the dry mass consists of polysaccharides, long-chain sugar compounds that swell in water and form mucilage. The thallus also contains lichen acids, which are responsible for the bitter taste. The European Pharmacopoeia requires a minimum swelling value of 4.5 for the herbal substance. Mucilage is a classic in European plant lore; another example is marshmallow.
| Group of substances | Examples | Content per EMA report | Characteristic |
|---|---|---|---|
| Mucilage (polysaccharides) | Lichenan (β-glucan), isolichenan (α-glucan), branched galactomannans | 25 to 50 % | Lichenan dissolves in hot water, isolichenan in cold water |
| Lichen acids | Fumarprotocetraric acid, protocetraric acid, protolichesterinic acid | Fumarprotocetraric acid 2.6 to 11.5 %, protolichesterinic acid 0.1 to 1.5 % (depending on collection site) | Bitter taste; poorly soluble in cold water |
| Usnic acid | Dibenzofuran derivative | only traces (about 0.04 %), not detected in other analyses | Considerably more common in many other lichens |
| Minerals and trace elements | Calcium, magnesium, iron; depending on location also lead and cadmium | depends on location | Lichens take up substances from the air |
Bitter, mucilaginous, mild: how Iceland moss tastes and is prepared
Anyone who brews Iceland moss notices two things quickly: the tea tastes bitter and becomes slightly slimy. Both come from the constituents. The lichen acids hardly dissolve in cold water, while the mucilage dissolves partly in hot and partly in cold water. Tradition therefore knows two routes: the hot infusion or decoction, and the cold extract, which is drunk shortly after preparation. The bitter substances are also the reason the lichen was traditionally used as a bitter herb before meals. More on this group of substances can be found in the article on bitter substances; another example of a bitter plant in the European herbal tradition is dandelion root.
The following details come from the EMA report and describe the traditional preparation, not a recommendation for an individual case.
| Form | Traditional specification | Note |
|---|---|---|
| Tea or cold extract (for irritation of mouth and throat) | 1.5 g of chopped lichen in 150 ml of boiling water, 3 to 4 times daily; drink the cold extract straight after preparation | For adults and adolescents from 12 years |
| Tea (for temporary loss of appetite) | 1 to 2 g in 150 ml of water, 3 times daily, as infusion or decoction | Adults only |
| Lozenges with aqueous extract | Lozenges on the market typically contain about 80 to 100 mg of extract; 1 to 2 lozenges several times daily | Not under 6 years, because of the dosage form |
The EMA's Committee on Herbal Medicinal Products (HMPC) classifies these uses as "traditional use": on the basis of at least 30 years of use, at least 15 of them in the EU, it considers the use of the mucilage-containing herbal substance for irritation of the mouth and throat with dry cough, and in adults for temporary loss of appetite, to be plausible. It does not see proof of efficacy in the strict sense.
And the research? A few observations on the side
The body of studies is modest, which is what makes it short to tell. A small study by Kempe and colleagues (1997; randomised dose-comparison study without placebo, around 60 adults) gave lozenges with aqueous extract to patients who had to breathe through the mouth after nasal surgery. The dry, irritated oral mucosa improved over five days in all dose groups, with no adverse effects reported. Whether this was due to the lichen or to natural recovery cannot be said without a placebo group.
In the laboratory, research focuses on the mucilage. An Icelandic team isolated a branched galactomannan from the lichen in 1994 that increased the uptake activity of white blood cells in cell experiments (in vitro; plus a mouse experiment with injection, animal study). A 2006 study on human immune cells (in vitro) showed that lichenan increased the release of the messengers IL-10 and IL-12p40. These are findings from cell cultures and say little about a cup of tea.
What to know before brewing: safety and origin
Tolerability. In the available studies, no or only mild, temporary complaints were reported. In people prone to contact allergies or light sensitivity, skin tests (Thune and Solberg, 1980; cited in the EMA report) showed allergic reactions to lichens. Use is excluded in cases of known hypersensitivity to the lichen.
Pregnancy, breastfeeding and children. Safety data for pregnancy and breastfeeding are lacking, and the EMA does not recommend use. For children, age limits differ depending on the dosage form, and the data are limited. Medical advice is sensible here.
Interactions. None are known. As a precaution, the EMA recommends an interval of half an hour to one hour from other medicines, because mucilage could delay their absorption. This has not been confirmed.
Contaminants. Lichens react sensitively to air pollution and accumulate substances from their surroundings. Samples from southern Finland contained raised levels of lead, cadmium and mercury. After the Chernobyl reactor accident, material from Scandinavia with low radioactivity was temporarily hard to obtain; this has improved since 1994. The European Pharmacopoeia limits the lead content to 10 ppm. The lichen is also listed in the EFSA compendium of plants with possible concerns, because of its lichen substances and its ability to accumulate heavy metals. Origin and tested quality therefore count for more than with many other herbs. An old feeding experiment with 50 % untreated lichen in the diet was toxic to mice; at usual amounts the committee does not expect such effects.
Duration. Without medical advice, use is limited to one week at most. In case of shortness of breath, fever or purulent sputum, a doctor should be consulted.
Conclusion: a frugal lichen with a lot of history
Iceland moss is a good example of European plant lore based on experience: an inconspicuous lichen from the north and the mountains that found its place in the kitchen and in the pharmacopoeias as emergency food, bitter herb and mucilage-containing herbal substance. Its appearance, distribution, constituents and preparation are well described. Research, by contrast, is modest: one small human study without a placebo comparison and laboratory work that cannot be transferred to everyday life. Anyone using the lichen should look for tested origin and heed the notes on pregnancy, children and duration of use.
This article serves as general information about Iceland moss and does not replace medical advice, diagnosis or treatment. If you have health complaints, please consult a doctor or pharmacist.
Sources
- European Medicines Agency (EMA), HMPC: Final assessment report on Cetraria islandica (L.) Acharius s.l., thallus, EMA/HMPC/36866/2014 (2015).
- European Medicines Agency (EMA), HMPC: European Union herbal monograph on Cetraria islandica (L.) Acharius s.l., thallus, EMA/HMPC/678891/2013 (2015).
- European Medicines Agency (EMA): Lichen islandicus – herbal medicinal product, overview page with summary for the public (EMA/812331/2016).
- Kempe C, Grüning H, Stasche N, Hörmann K. Icelandic moss for prevention and treatment of inflammation and dryness of the oral mucosa. Laryngorhinootologie 1997;76(3):186–188. doi:10.1055/s-2007-997409 (randomised dose-comparison study, human).
- Ingólfsdóttir K, Jurcic K, Fischer B, Wagner H. Immunologically active polysaccharide from Cetraria islandica. Planta Med 1994;60(6):527–531. doi:10.1055/s-2006-959564 (in vitro and animal study).
- Omarsdottir S, Olafsdottir ES, Freysdottir J. Immunomodulating effects of lichen-derived polysaccharides on monocyte-derived dendritic cells. Int Immunopharmacol 2006;6:1642–1650. Search in PubMed (in vitro).
- Olafsdottir ES, Ingólfsdóttir K. Polysaccharides from lichens: structural characteristics and biological activity. Planta Med 2001;67:199–208. doi:10.1055/s-2001-12012 (narrative review).
