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Agaricus subrufescens (syn. Agaricus blazei, Agaricus brasiliensis or Agaricus rufotegulis) is a species of mushroom, commonly known as almond mushroom, mushroom of the sun, God's mushroom, mushroom of life, royal sun agaricus, jisongrong, or himematsutake (Chinese: 杏仁松茸, Japanese: 姫まつたけ, "princess matsutake") and by a number of other names. Agaricus subrufescens is a choice edible, with a somewhat sweet taste and fragrance of almonds. The fungus is also well known as a medicinal mushroom, for its purported medicinal properties, due to research which indicates it may stimulate the immune system.
Agaricus subrufescens was first described by the American botanist Charles Horton Peck in 1893. During the late 19th and early 20th centuries, it was cultivated for the table in the eastern United States. It was discovered again in Brazil during the 1970s, and misidentified as Agaricus blazei Murrill, a species originally described from Florida. It was soon marketed for its purported medicinal properties under various names, including ABM (for Agaricus blazei Murrill), cogumelo do sol (mushroom of the sun), cogumelo de Deus (mushroom of God), cogumelo de vida (mushroom of life), himematsutake, royal sun agaricus, Mandelpilz, and almond mushroom.
In 2002, Didukh and Wasser correctly rejected the name A. blazei for this species, but unfortunately called the Brazilian fungus A. brasiliensis, a name that had already been used for a different species, Agaricus brasiliensis Fr. (1830). Richard Kerrigan undertook genetic and interfertility testing on several fungal strains, and showed that samples of the Brazilian strains called A. blazei and A. brasiliensis were genetically similar to, and interfertile with, North American populations of Agaricus subrufescens. These tests also found European samples called A. rufotegulis to be of the same species. Because A. subrufescens is the oldest name, it has taxonomical priority.
Note that Agaricus blazei Murrill is a perfectly valid name, but for a completely different mushroom. Agaricus silvaticus is also a perfectly valid name for a common, north temperate, woodland mushroom. Neither is a synonym of Agaricus subrufescens.
The cap is initially hemispherical, later becoming convex, with a diameter of 5 to 18 cm (2.0 to 7.1 in). The cap surface is covered with silk-like fibers, although in maturity it develops small scales (squamulose). The color of the cap may range from white to grayish or dull reddish brown; the cap margin typically splits with age. The flesh of A. subrufescens is white, and has the taste of "green nuts", with the odor of almonds. The gills are not attached to the stalk (free), narrow, and crowded closely together. They start out whitish in color, then later pinkish and finally black-brown as the spores mature. Spores are ellipsoid, smooth, dark purplish-brown when viewed microscopically, with dimensions of 6–7.5 by 4–5 µm. The stipe is 6 to 15 cm (2.4 to 5.9 in) by 1 to 1.5 cm (0.4 to 0.6 in) thick, and bulbous at the base. Initially solid, the stipe becomes hollow with age; it is cottony (floccose) to scaly towards the base. The annulus is abundant and double-layered; it is bent downwards towards the stem, smooth and whitish on the upper side, and covered with cottony scales on the lower side.
Agaricus subrufescens forms fruitbodies singly or in clusters in leaf litter in rich soil, often in domestic habitats. Originally described from the northeastern United States and Canada, it has been found growing in California, Hawaii, Great Britain, the Netherlands, Taiwan, Philippines, Australia and Brazil.
Agaricus subrufescens is a choice edible, with a somewhat sweet taste and fragrance of almonds. The almond smell of the mushroom is mostly due to the presence of benzaldehyde, benzyl alcohol, benzonitrile, and methyl benzoate.
Because Agaricus subrufescens contains a high level of beta glucans, compounds known for stimulating the immune system, the fungus is used in oncological therapy in Japan and Brazil. In addition to beta glucans, the mushroom's effect on the immune system is believed to be due to other polysaccharides, such as alpha glucans. In Japan, Agaricus subrufescens is sold under the brand names KingAgaricus 100, Sen-Sei-Ro Gold, and ABMK, and is used by an estimated 500,000 people In Japan, Agaricus subrufescens is also the most popular complementary and alternative medicine used by cancer patients. Although Agaricus subrufescens is cultivated in the United States, the largest exporters are China and Brazil. As noted in a scientific review of A. subrufescens research, the range of quality in A. subrufescens cultivation can affect the mushroom's ability to impact cells of the immune system.
Recently, Tetsuo Watanabe published a report in the Biological and Pharmaceutical Bulletin on a novel hybrid of A. subrufescens called Basidiomycetes-X (BDM-X) and a US patent was issued on a novel hybrid of the A. subrufescens edible mushroom which was crossbred (hybridized) with another medicinal mushroom, resulting in a new hybrid claimed to possess 10 to 3000 times the potency of similar but unpatented mushrooms.