The reishi or lingzhi mushroom is a polypore mushroom belonging to the genus Ganoderma. Its red-varnished, kidney-shaped cap gives it a distinct appearance. When fresh, the lingzhi is soft, cork-like, and flat. It lacks gills on its underside, and instead releases its spores via fine pores. Depending on the age of the mushroom, the pores on its underside may be white or brown.
Lingzhi mushroom is used in traditional Chinese medicine. In nature, it grows at the base and stumps of deciduous trees, especially that of the maple. Only two or three out of 10,000 such aged trees will have lingzhi growth, and therefore its wild form is extremely rare. Today, lingzhi is effectively cultivated on hardwood logs or sawdust/woodchips.
Ganoderma lucidum produces a group of triterpenes called ganoderic acids, which have a molecular structure similar to that of steroid hormones. It also contains other compounds often found in fungal materials, including polysaccharides (such as beta-glucan), coumarin, mannitol, and alkaloids. Sterols isolated from the mushroom include ganoderol, ganoderenic acid, ganoderiol, ganodermanontriol, lucidadiol, and ganodermadiol.
A 2015 Cochrane database review found insufficient evidence to justify the use of G. lucidum as a first-line cancer treatment. It suggests that G. lucidum may have “benefit as an alternative adjunct to conventional treatment in consideration of its potential of enhancing tumour response and stimulating host immunity.” Existing studies do not support the use of G. lucidum for treatment of risk factors of cardiovascular disease in people with type 2 diabetes mellitus.
Because of its bitter taste, lingzhi is traditionally prepared as a hot water extract product. Thinly sliced or pulverized lingzhi (either fresh or dried) is added to boiling water which is then reduced to a simmer, covered, and left for 2 hours. The resulting liquid is dark and fairly bitter in taste. The red lingzhi is often more bitter than the black. The process is sometimes repeated to increase the concentration. Alternatively, it can be used as an ingredient in a formula decoction, or used to make an extract (in liquid, capsule, or powder form). The more active red forms of lingzhi are far too bitter to be consumed in a soup.
Lingzhi is now commercially manufactured and sold. Since the early 1970s, most lingzhi is cultivated. Lingzhi can grow on substrates such as sawdust, grain, and wood logs. After formation of the fruiting body, lingzhi is most commonly harvested, dried, ground, and processed into tablets or capsules to be directly ingested or made into tea or soup. Other lingzhi products include processed fungal mycelia or spores.