The shiitake (Lentinula edodes) is an edible mushroom native to East Asia, which is cultivated and consumed in many Asian countries. It is also considered a medicinal mushroom in some forms of traditional medicine.

Taxonomy and naming
The mushroom's Japanese name shiitake is composed of shii, the name of the tree Castanopsis cuspidata that provides the dead logs on which it is typically cultivated, and take meaning 'mushroom'.

It is also commonly called "Sawtooth oak mushroom", "black forest mushroom", "black mushroom", "golden oak mushroom", or "oakwood mushroom".

The species was formerly known as Lentinus edodes and Agaricus edodes. The latter name was first applied by the English botanist Miles Joseph Berkeley in 1878.

Cultivation history
Shiitake are native to Japan, China and Korea and have been grown in all three countries since prehistoric times. The oldest record regarding the shiitake mushroom dates back to AD 199 at the time of Emperor Chuai in Japan. The first written record of shiitake cultivation can be traced to Wu Sang Kwuang in China, born during the Song Dynasty (AD 960-1127).

During the Ming Dynasty (AD 1368-1644), physician Wu Juei wrote that the mushroom could be used not only as a food but as a medicinal mushroom, taken as a remedy for upper respiratory diseases, poor blood circulation, liver trouble, exhaustion and weakness, and to boost qi, or life energy. It was also believed to prevent premature aging.

The Japanese cultivated the mushroom by cutting shii trees with axes and placing the logs by trees that were already growing shiitake or contained shiitake spores. Before 1982, the Japanese variety of these mushrooms could only be grown in traditional locations using ancient methods. In 1982, Gary F. Leatham published an academic paper based on his research on the budding and growth of the Japan Islands variety; the work helped make commercial cultivation possible in the United States.

In 1974, total production was estimated at about 143 000 tonnes, with Japan representing 94.5% of the total, China 4.2%, Taiwan 1.1%, and South Korea 0.2%. in 1997 China's shiitake production had risen from 4.2% to 85.1%.

Culinary use
Fresh and dried shiitake have many uses in the cuisines of East Asia. In Japan, they are served in miso soup, used as the basis for a kind of vegetarian dashi, and also as an ingredient in many steamed and simmered dishes. In Chinese cuisine, they are often sauteed in vegetarian dishes such as Buddha's delight. In Thailand, they may be served either fried or steamed.

Shiitake are also dried and sold as preserved food. These are rehydrated by soaking in water before using. Many people prefer dried shiitake to fresh, considering that the sun-drying process draws out the umami flavour from the dried mushrooms. The stems of shiitake are rarely used in Japanese and other cuisines, primarily because the stems are harder and take longer to cook than the soft fleshy caps.

One type of high grade shiitake is called donko in Japanese and donggu in Chinese, literally "winter mushroom". Another high grade of mushroom is called huagu in Chinese, literally "flower mushroom", which has a flower-like cracking pattern on the mushroom's upper surface. Both of these are produced at lower temperatures.

Today, shiitake mushrooms have become popular in other countries as well. Russia produces and also consumes large amounts of them, mostly sold pickled; and the shiitake is slowly making its way into western cuisine as well. There is a global industry in shiitake production, with local farms in most western countries in addition to large scale importation from China, Japan, Korea and elsewhere.

Like all mushrooms, shiitakes produce vitamin D2 upon exposure of the ergosterol to the UVB rays of sunlight or broadband UVB fluorescent tubes.

While all mushrooms have ergosterol in and the potential to produce vitamin D2 in such a manner, the transparent white of the shiitake gills permits greater contact of the UVB with ergosterol and very high D2 values can be achieved with exposure to broadband UVB fluorescent tubes.

Preliminary research
Basic research has evaluated whether consumption of shiitake mushrooms may affect the immune system, possess antibacterial properties, reduce platelet aggregation, or possess antiviral properties, possibly through protease inhibitors.

Active Hexose Correlated Compound (AHCC) is an α-glucan-rich compound isolated from shiitake. In Japan, AHCC is the second most popular complementary and alternative medicine used by cancer patients and is metabolized via the CYP450 2D6 pathway. Eritadenine, an isolate of the mushroom, is an inhibitor of S-adenosyl-L-homocysteine hydrolase (SAHH) and has hypocholesterolemic activity.

Other basic research tested if AHCC may increase the body's resistance to pathogens as shown in experiments with the influenza virus, West Nile virus, or bacterial infection. Animal research and limited clinical trials indicate that AHCC may enhance immune function. Other basic research has shown that AHCC may affect hepatocellular carcinoma and prostate cancer.

Rarely, consumption of raw or slightly cooked shiitake mushrooms may evoke signs of allergy, including "an erythematous, micro-papular, streaky, extremely pruriginous rash" that occurs all over the body including face and scalp, appearing about 48 hours after consumption and disappearing after several days. This effect, presumably caused by the polysaccharide lentinan, is known in Asia, but is unfamiliar to Europeans. Although it may occur in roughly 2% of the population, thorough cooking may eliminate allergenicity