Never eat a wild mushroom identified only from a website, a book or an app. Have every find checked in person by an expert, such as a mycological society.
Identification
Agaricus subrufescens has a cap 5–15 cm across, convex then flattened, whitish to golden or reddish-brown with fine fibrous scales. The gills are free from the stem, whitish in young buttons, then pinkish and finally dark chocolate brown. The robust white stem carries a large, pendant ring with a cogwheel-like lower surface. The flesh is white and may stain slightly yellowish when bruised.
The most useful field character is the strong sweet smell of almonds or marzipan, caused by benzaldehyde and related compounds. The spore print is dark brown. Several names have been applied to this species, including Agaricus blazei (a misapplied name in the trade), Agaricus brasiliensis and Agaricus rufotegulis; DNA studies showed that Brazilian cultivated material belongs to A. subrufescens, first described from North America.
Habitat and ecology
The almond mushroom is a saprotroph of rich soils, leaf litter, compost and manured ground. It is known from North and South America, and has been reported from Europe, Asia and Hawaii, mostly in warm conditions. Fruiting occurs in summer and autumn, or in rainy seasons in subtropical regions. Many modern populations are associated with human-modified habitats such as gardens and compost heaps.
Uses and importance
The almond mushroom is a good culinary mushroom with a sweet aroma, used like button mushrooms. It was cultivated in North America in the late nineteenth century, and from the 1960s and 70s strains from Brazil were developed in Japan, where it became popular as a health product.
Research has studied its polysaccharides, especially beta-glucans, in cell cultures and animals, where they influenced immune parameters; a small number of human studies exist, with limited and inconsistent results. Isolated case reports have described liver injury in people taking extracts, and like other Agaricus species it contains agaritine. There is no proof that it prevents or cures disease. In the EU, mushroom supplements are regulated as food, and health claims may only be used if authorised under Regulation (EC) No 1924/2006. Consult a doctor before taking supplements, especially with liver disease or medication.
Cultivation
Cultivation resembles that of the button mushroom: a straw-based compost is prepared, pasteurised and spawned, then covered with a casing layer. The almond mushroom needs higher temperatures, with spawn run around 25–28 °C and fruiting at roughly 22–26 °C, and high humidity. It is produced commercially in Brazil, China and Japan, mostly for drying and extracts. Yields are lower and more variable than with button mushrooms, so it remains a specialty crop.
Safety and edibility
The almond mushroom is edible when correctly identified and cooked. Because of agaritine and case reports involving extracts, eat it in normal food amounts rather than daily large doses, and talk to a doctor before using supplements.
Never eat a wild mushroom based on a website or photo. Wild Agaricus must be confirmed in person by an expert such as a mycological society or trained mushroom adviser. Deadly white Amanitas, especially Amanita phalloides and Amanita virosa, can be confused with young Agaricus; the yellow-staining Agaricus xanthodermus is toxic.
If you suspect mushroom poisoning, call your local emergency number or poison centre straight away, even before any symptoms appear, and keep the remains of the mushrooms.
Look-alikes
The edible horse mushroom, Agaricus arvensis, and other yellowing Agaricus also smell of almonds or aniseed but differ in microscopic features and habitat. Agaricus xanthodermus stains intense chrome-yellow at the stem base and smells of ink or phenol. Deadly Amanita species have white gills, a white spore print and a volva at the base.
Around the world
Globally, most almond mushrooms on the market are grown in Brazil and Asia and sold dried, powdered or as extracts. Products labelled Agaricus blazei, ABM or himematsutake usually refer to this species, but authenticity and quality vary, so species verification and contaminant testing are important.
