Mosses (division Bryophyta) are non-vascular plants that form dense green mats in damp, shady environments. They are not considered a food source for humans and are structurally and chemically ill-suited for the digestive system. Consuming moss will often cause adverse physical reactions and is potentially harmful.
The Mechanical Challenges of Consuming Moss
Eating moss presents immediate physical and digestive hurdles because of the plant’s rigid cellular structure. Moss contains a high percentage of indigestible fibers, including cellulose and hemicellulose, which our bodies lack the necessary enzymes to break down. This tough consistency means that consuming moss offers virtually no nutritional energy to humans.
The high bulk of the undigested plant material travels through the gastrointestinal tract largely unchanged, which can cause significant digestive distress. Ingestion may lead to symptoms like bloating, gas, and stomach cramps as the gut struggles to process the fiber. In large quantities, the compact nature of moss creates a risk of obstruction or impaction in the digestive system.
Toxins, Heavy Metals, and Pathogen Risk
Beyond the issue of indigestibility, moss poses various chemical and biological safety risks. Many moss species naturally produce chemical compounds, such as certain terpenoids and phenols, as a defense mechanism against pests and microbes. When ingested by humans, these compounds can act as irritants, leading to acute symptoms like vomiting, diarrhea, or other forms of gastrointestinal poisoning.
A more pervasive danger is moss’s function as a bioaccumulator of environmental contaminants. Mosses lack true roots, meaning they absorb water and nutrients primarily from the atmosphere and surface water directly through their leaves. This structure allows them to efficiently absorb and concentrate heavy metals and other pollutants from the environment. Studies use mosses as bioindicators because they can harbor high levels of toxic elements, including lead, cadmium, arsenic, and mercury. Furthermore, the consistently moist and dense environment of moss mats is an ideal breeding ground for bacteria, parasites, and other pathogens, introducing a risk of microbial infection upon consumption.
The Few Species Used Traditionally or Edibly
The few “moss-like” species that have been historically consumed are almost always lichens, not true mosses (Bryophyta). These lichens, such as Iceland Moss (Cetraria islandica) and Reindeer Moss (Cladonia rangiferina), are symbiotic organisms of a fungus and an algae, which are often mistakenly called moss. Iceland Moss, for example, was used in Northern European cultures as a famine food, often mixed with flour to make bread.
The consumption of these lichens requires extensive and specialized preparation to make them safe and palatable. Lichens contain lichen acids, which are bitter and can cause stomach upset if eaten raw. Preparation typically involves repeatedly soaking the lichen in water, sometimes with added bicarbonate of soda or wood ash, and then boiling it to leach out the bitter compounds. Only after this rigorous process, which neutralizes the acids and makes the carbohydrate content more digestible, can the lichen be safely consumed, often as a thickening agent or in a prepared soup or pudding.
Summary of Safety Takeaways
The risks associated with eating wild moss far outweigh any nutritional benefit. The primary dangers stem from the plant’s structural indigestibility and its capacity to concentrate environmental toxins. Mosses are highly efficient bioaccumulators of heavy metals, meaning they may contain dangerous levels of pollutants even in seemingly clean areas. The vast majority of species are unsuitable for human consumption, and the few exceptions are lichens that require extensive preparation to remove natural toxins. Wild moss should be avoided as a food source.