Agaricus macrosporus: The Ultimate Mushroom Guide
About The Agaricus macrosporus Mushroom
This small group of Macro Mushrooms (Agaricus urinascens / A.macrosporus) were found on a grassy roadside verge, not far from some fields and a small wooded area. They’re also found in similar environments such as pastures, woodland edges and grassy woodland clearings.
Unfortunately, maggots can spot this mushroom as well and almost all the Macro mushrooms are maggot ridden.
Agaricus macrosporus is a good edible species and can be used in any recipe calling for large cultivated (Portobello) mushrooms. It is great in risotto dishes and omelets, and it makes tasty soups and sauces to be served with meat.
Other names: Macro Mushroom.
Agaricus macrosporus Identification
Initially globose, the cap of Agaricus urinascens expands to become plano-convex and eventually flattens without an in-rolled margin, and the surface is radially fibrillose or scaly at maturity, white at first but becoming pale ochre and yellowing slightly, especially near the margin, when bruised. Caps grow to between 10 and 25cm diameter at maturity. When bruised, the cap surface slowly turns yellowish, most noticeably towards the margin.
Pale greyish pink when young, the crowded free somewhat undulating gills later become dark brown or purplish brown as the fruitbody ages. The gill edges are slightly paler than the gill faces.
The stem is 2 to 3.5cm in diameter and 7 to 12 cm long, fusiform to cylindrical with a slightly clavate base and a pendent membranous ring, the lower surface patterned like a cogwheel. Above the ring, the stem surface is smooth, while below it is girdled with white or slightly brownish scales in a rather irregular snakeskin-like pattern. When cut the stem flesh turns slightly brown, most markedly at the stem base.
Ellipsoidal, smooth, 8.5-12.3 x 5.2-6.9µm - larger than the spores of any other Agaricus species found in Britain.
Odor and Taste
When young the Macro Mushroom gives off a faint but pleasant smell of almonds, but as the fruitbody ages its smell becomes increasingly ammoniacal (or like urine, as its specific epithet suggests). The taste is very like that of the familiar commercial button mushroom (the cultivated form of Agaricus bisporus).
Habitat & Ecological role
Macro Mushrooms are saprobic and are most commonly seen in small groups in permanent pastures, on grassy roadside verges, on woodland edges, and in grassy woodland clearings.
There is a danger of confusing this mushroom with the deadly poisonous bulbous agaric Amanita phalloides and Amanita pantherina. Agaricus excellent is different by its taller and slimmer stipe which is striped lengthwise. Agaricus augustus does not have the pure white cap in young specimens.
Agaricus macrosporus Taxonomy & Etymology
A thoroughly modern mushroom, this species was described scientifically in 1938 by Danish mycologist Frits Hansen Møller (1887 - 1962) and German mycologist Julius Schäffer (1882 - 1944), when it was given the binomial scientific name Psalliota urinascens.
The scientific name Agaricus urinascens dates from a 1949 paper (published in 1951) by German-born American Rolf Singer.
Two varieties of this species are now recognised, and so the nominate variety is formally referred to as Agaricus urinascens var. urinascens.
Synonyms of Agaricus urinascens var. urinascens include Psalliota villatica, Psalliota arvensis ssp. macrospora F.H. Møller & Jul. Schäff., Psalliota urinascens F.H. Møller & Jul. Schäff., Agaricus macrosporus (F.H. Møller & Jul. Schäff.) Pilát, Agaricus urinascens (F.H. Møller & Jul. Schäff.) Singer, Psalliota macrospora (F.H. Møller & Jul. Schäff.) F.H. Møller, and Agaricus albertii Bon.
The specific epithet urinascens means 'gradually acquiring a smell like urine', while the common English name Macro Mushroom is a reference to the huge size (compared with other mushrooms in the Agaricus genus) of the spores of these mushrooms.
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