Identification
Ganoderma lingzhi forms kidney- to fan-shaped brackets that are usually attached to wood by a lateral, often shiny stalk. The upper surface looks varnished, reddish-brown to dark mahogany, with concentric zones and frequently a yellowish to whitish growing margin. The underside is covered with tiny whitish to cream pores that bruise brown. The flesh is corky to woody and pale brown, and the spores are brown, with a characteristic double wall visible under the microscope.
The naming is important. For decades, cultivated East Asian reishi was sold as Ganoderma lucidum, a name based on a European species. Molecular studies published from 2012 onwards showed that the main cultivated lingzhi of China and East Asia is a distinct species, described as Ganoderma lingzhi; some authors treat it as identical with Ganoderma sichuanense. True Ganoderma lucidum is a European and western Asian species. Many products and studies still use the older name, so labels should be interpreted with care.
Habitat and ecology
In the wild, Ganoderma lingzhi is a white-rot fungus that decays the wood of broadleaf trees, growing on stumps, roots and trunks in East Asia. Like other Ganoderma species, it can act as a weak parasite of living trees and as a decomposer of dead wood, returning carbon and nutrients to the soil.
Wild fruit bodies are relatively scarce, which is why traditional texts describe lingzhi as precious. Almost all reishi on the market today comes from cultivation, mainly in China, Korea, Japan and other parts of Asia.
Uses and importance
Lingzhi has a long history in Chinese and other East Asian traditional medicine. It is sold today as dried slices, teas, powders, extracts of fruit bodies or mycelium, and spore powder.
Research has focused on polysaccharides (including beta-glucans) and triterpenoids (such as ganoderic acids). In cell and animal studies, these compounds have shown effects on immune cells, inflammation, oxidative stress and tumor cell growth. Human evidence is much weaker. A Cochrane systematic review of five small randomized trials in people with cancer, all from China and of generally unsatisfactory methodological quality, did not find sufficient evidence to justify its use as a first-line cancer treatment and could not show an effect on long-term survival. Small trials on other outcomes have produced mixed results.
Laboratory findings cannot be transferred directly to people, and product composition varies widely between fruit body, mycelium and spore preparations.
Cultivation
Lingzhi is cultivated on hardwood logs (often short, sterilized log sections that are buried in soil after colonization) or on supplemented hardwood sawdust in bags or bottles. It needs warm conditions for fruiting, high humidity and fresh air; at high carbon dioxide levels it forms branched, antler-like fruit bodies instead of brackets. Crop cycles take several months. Cultivation is of moderate difficulty and is well suited to small producers, but quality control, species authentication and contaminant testing are essential for any product sold to consumers.
Safety and edibility
Reishi is not a culinary mushroom: it is too woody to eat and is used as tea, powder or extract. Clinical trials report it as generally well tolerated, with occasional mild effects such as digestive upset, dry mouth or skin reactions. Isolated case reports of liver injury associated with reishi products have been published.
Because laboratory studies suggest effects on blood clotting, blood pressure, blood sugar and the immune system, people who take medication (for example anticoagulants, antihypertensives or diabetes drugs), who are pregnant or breastfeeding, or who are awaiting surgery should consult a doctor before using reishi products. Reishi supplements are not a substitute for medical treatment.
In the European Union, mushroom supplements are regulated as foods, and no health claim for reishi has been authorized; products may not claim to prevent, treat or cure disease. Quality varies, and mislabelling and contamination with heavy metals have been reported in the supplement market generally, so choose products with independent testing.
If you suspect mushroom poisoning, call Poison Help at 1-800-222-1222 or 911 in an emergency straight away, even before symptoms appear, and keep the remains of the mushrooms.
Look-alikes
Several Ganoderma species look similar. The European Ganoderma lucidum is very close in appearance; Ganoderma resinaceum is larger, with a less pronounced stalk; and Ganoderma tsugae grows on conifers in North America. The artist's bracket (Ganoderma applanatum) and Ganoderma australe have a dull, matt upper surface rather than a varnished one. Separating them reliably requires microscopy or DNA analysis, which is also how supplement manufacturers should authenticate raw material.
In the United States
Ganoderma lingzhi is an East Asian species. American "reishi" foragers find related native species, such as the hemlock varnish shelf (Ganoderma tsugae) on eastern hemlock, G. sessile on hardwoods in the East and G. oregonense on conifers in the West.
In the US, reishi products are sold as dietary supplements, which the FDA does not approve before marketing and which may not claim to treat or prevent disease.