Hericium erinaceus

Hericium erinaceus (also called lion's mane mushroom, monkey head mushroom, bearded tooth mushroom, satyr's beard, bearded hedgehog mushroom, pom pom mushroom, or bearded tooth fungus) is an edible mushroom belonging to the tooth fungus group. Native to North America, Europe and Asia, it can be identified by its long spines (greater than 1 cm length), occurrence on hardwoods, and tendency to grow a single clump of dangling spines. The fruit bodies can be harvested for culinary use. There is no high-quality evidence from clinical research to indicate that lion's mane mushroom has medicinal properties.
"Hericium erinaceus" can be mistaken for other species of "Hericium", which grow across the same range. In the wild, these mushrooms are common during late summer and fall on hardwoods, particularly American beech. Usually "H. erinaceus" is considered saprophytic, as it mostly feeds on dead trees. However, it can also be found on living trees, so may be a tree parasite as well. This could indicate an endophytic habitat.
Common names.
Both the Latin genus name ' and the species name ' mean 'hedgehog' in Latin. This is also reflected by the German name, "Igel-Stachelbart" (literally, "hedgehog goatee"), and some of its common English names, such as "bearded hedgehog" and "hedgehog mushroom".
Morphology.
The fruitbodies of "H. erinaceus" are large, irregular bulbous tubercules. They are 5–40 cm in diameter, and are dominated by crowded, hanging, spore-producing spines, which are 1–4 cm long. Fruit bodies and spines colour are white to cream, but can turn yellow-brown when older.
The hyphal system is monomitic, amyloid, and composed of thin- to thick-walled hyphae that are about 3–15 microns (um) wide. The hyphae also contain clamped septa and gloeoplerous elements (filled with oily, resinous substances), which can come into the hymenium as gloeocystidia.
The basidia are 25–40 um long and 5–7 um wide, contain four spores each and possess a basal clamp. The white amyloid basidiospores measure around 5–7 um in length and 4–5 um in width. The spore shape is described as subglobose to short ellipsoid and the spore surface is smooth to finely roughened.
Development.
The fruitbodies of "H. erinaceus" are mainly produced annually from August to November in Europe. It was observed that "H. erinaceus" could fruit intermittently for 20 years on the same dead tree. It is hypothesized that "H. erinaceus" can survive for 40 years. The mating system of "H. erinaceus" species found in the USA was shown to be bifactorially heterothallic.
The monokaryotic mycelium growth of "H.erinaceus" is slower than dikaryotic growth and only about a low percentage of monokaryotic cultures yield fruitbodies. Monokaryotic fruitbodies are also smaller than dikaryotic fruitbodies. The monokaryotic mycelium was found to produce fusoid to subglobose chlamydospores of 6–8 x 8–10 um size. These spores can stay viable for more than seven years and be stored under anaerobic conditions. Chlamydospore germination requires 30 to 52 hours, with a germination success rate of 32 to 54%.
Spore production is highest at midday, relative to temperature increase and relative humidity decrease. Daily trends towards lower relative humidity can favor sporulation, however levels of relative humidity that are too low do not favor high total spore production.
Distribution.
"Hericium" species can be found throughout the northern hemisphere. "Hericium erinaceus" has been used in traditional Chinese medicine for centuries and its production is widespread within Asia, mostly using extensive production practices on wood logs or stumps.
Despite its higher prevalence in Asia, "H. erinaceus" was first described in North America. Its production there occurs only on a small scale. Most of it is intensive indoor production with only a few small outdoor sites where log cultivation is practiced. Three "Hericium" species can be found in eastern North America, one being "H. erinaceus", the other two "H. americanum" and "H.coralloides."
Although "H. erinaceus" is native to Europe, it has been red listed in 13 European countries due to poor germination and establishment. This specific genus fruits between August and December in the United Kingdom, and will continue to produce spores until as late as February in the following year. It is able to withstand cold temperatures and frost conditions.
Strains and yield.
In fungi cultivation, fungal strains are analogous to plant varieties in crop breeding. Fungal strains comprise clonal descendants of a single isolation from one fungal colony in a pure culture. "Hericium" spp. grow in the wild in North America, Europe and Asia and, although there is considerable scientific research about them, they are not commonly industrially produced. Accordingly, there are few commercially available strains in the USA or Europe and little or no breeding for higher yield or other favorable traits has occurred. Production trials in Egypt report yields of "H.erinaceus" averaging at 165g per 1 kg medium.
Uses.
"Hericium erinaceus" produces edible fruiting bodies that have uses as food and in traditional medicine.
Culinary use.
"Hericium erinaceus" is common in gourmet cooking. Alongside shiitake ("Lentinus edodes") and oyster ("Pleurotus ostreatus") mushrooms, "H. erinaceus" is used as a specialty mushroom. Its flavor may be compared to that of lobster. The production of specialty mushrooms in the USA increased by about 23% between 2010 and 2018 from 16 to 20 million lbs (7–9 million kg). This increasing consumer interest in specialty mushrooms has encouraged the improvement of shiitake strains.
"H. erinaceus" fruiting bodies contain 57% carbohydrates (8% as dietary fiber), 4% fat, and 22% protein.
Medicinal Use.
"Hericium erinaceus" has been used in traditional Chinese medicine.
"H. erinaceus" contains diverse phytochemicals, including polysaccharides, such as β-glucan, as well as hericenones and erinacines. Other compounds include hexadecanoic acid (26%), linoleic acid (13.1%), phenylacetaldehyde (8.9%) and benzaldehyde (3%), and volatile oils, such as 2-methyl-3-furanthiol, 2-ethylpyrazine and 2,6-diethylpyrazine. Low concentrations of ergosterol are present.
Ecology.
Disease.
"Brennandania lambi" (Acari: ) is a mite pest of fungi culture in China. This mite can develop and reproduce on the mycelium of "H. erinaceus". Farm hygiene and heating treatments are the most important pest management strategies that should be done to counter this acari.
Competition with other fungi.
"Hericium" species are good competitors against other wood colonisers. They show the ability to maintain their place on dead wood, also when confronted with secondary colonizers like "Trametes versicolor" and "Stereum hirsutum". "Hericium erinaceus" has shown to be slightly more competitive than other fungi tooth species including "Creolophus cirrhatus" and "Hericium coralloides."
Cultivation.
Substrate requirements.
As a saprophyte that occurs on dead wood, "H. erinaceus" requires adequate substrate factors, including suitable carbon and nitrogen sources, a certain pH value and ideal carbon/nitrogen ratio. 
Many different substrates have been successfully used for this mushroom cultivation. Depending on the type of cultivation, the substrate can be either solid (artificial log) or liquid (submerged culture and deep submerged culture). 
The solid substrate is most commonly a mixture of sawdust of hardwood or conifer containing different complements that may include wheat bran, wheat straw, soybean meal, corn meal, rice bran and rice straw. For example, "H. erinaceus" strains grow on beech sawdust substrate enriched with wheat bran (20%), rye grain (25%), soybean meal (7%), rapeseed meal (10%) or meat-osseous flour (6%). 
An example of a liquid substrate composition can be glucose for the carbon source, soybean powder, corn powder, and wheat bran powder as a complex nitrogen source. The pH values most suitable for the favorable growth of "H. erinaceus" were in the range of 5.0 - 9.0, with pH 6.0 as optimal.
Climate requirements.
"H. erinaceus" requires a humid environment for its growth: 85 to 90% of relative humidity in the air. The incubation temperature most suitable for the mycelial growth of "H. erinaceus" was found to be 25 °C, and the optimum temperature for vegetative growth was 26 °C. "H. erinaceus" is unable to grow with a water potential lower than -5 Mpa.
Cultivation techniques.
The artificial cultivation of "H. erinaceus" was first reported in China in 1988. It is cultivated using artificial logs, bottles and polypropylene bags. However, this type of artificial cultivation is not suitable for industrialized production due to its low yield and long cultivation cycles.
Submerged culture is a type of artificial cultivation of "H. erinaceus" whereby the fungus is grown in a liquid medium. Using this method, a large number of mycelia can be obtained quickly. Bioactive compounds can be sourced from the fruiting bodies, submerged-cultivated mycelial biomass or liquid-cultivated broth. Growers optimize the culture medium composition to obtain simultaneously high yields of "H. erinaceus" mycelial biomass, exopolysaccharides, and polysaccharides. Submerged fermentation is preferable for the production of mycelial biomass and biologically active metabolites in order to produce a more uniform biomass and extract products.
Growth regulators, such as 2,4-Dichlorophenoxyacetic acid and gibberellin, were observed to have an advantageous impact on spore germination. Other technologies, like red and green laser light of low intensity, stimulated spore germination as well as the vegetative growth of mycelium. Argon and helium lasers also contributed to the acceleration of fruit body development by 36–51%.
Wild strains.
Wild strains of "Hericium" spp. can be isolated and cultivated by first gathering fruiting bodies from fallen trees in the natural habitat. The fruiting bodies can then be opened to attain pieces of their inner spore-producing tissue. This tissue is then placed onto petri dishes with agar to cultivate fungal colonies at 25 °C. After several transfers to new petri dishes to verify the purity of the strain, it can be kept at -80 °C for long-term storage.