Facial cystidia: absent.
Basidia: 2-spored.
Habitat & Distribution: Frequent on manure heaps, straw heaps, on road scrapings and around garden plants.
General Information: This fungus is recognised by the dark fibrils on the cap, the 2-spored basidia easily seen with the low power of a microscope, and the pink gills when young. Much confusion has existed over this fungus and its nearest relatives. It is similar to the ‘Cultivated mushroom’, A. hortensis (Cooke) Pilát, which is offered for sale in shops. However, it differs in several minor details and it may be that A. bisporus is the fungus from which the cultivated mushroom developed, very probably unconsciously by man, but the history of the cultivated mushroom is very obscure. The cultivated mushroom when bought in British shops is white but in the United States two varieties are sold, one with the brownish fibrils predominating and a snow-white one where the fibrils do not darken; the former is frequently found in Europe. The white form is sometimes found in gardens where spent-mushroom spawn is used as mulching around fruit-trees but it has a rounder cap than A. bisporus. The cultivated mushroom accounts for an annual income of £14 million in the British Isles.
Illustrations: A. hortensis—LH 133 (as the forma albida); NB 317; WD 711. A. bisporus—Hvass 161; LH 133.
Plate 43. Fleshy fungi: Spores purple-brown and borne on gills
![[Larger illustration]](#467779198995390083_illo134lg.png.id-7615777255677330930.wrap-0.html.html){kind=link}