Agaricus bitorquis
Agaricus bitorquis is an edible white mushroom of the genus "Agaricus", similar to the common button mushroom that is sold commercially. The name supersedes "Agaricus rodmani". It is also commonly known as torq, the banded agaric, spring agaric, or pavement mushroom, as it has been recorded pushing up paving slabs. Taxonomy. The specific epithet "bitorquis" is Latin "having two collars", and refers to the two rings resulting from detachment of the veil from both the top and bottom of the stipe. The species was first defined by the French mycologist Lucien Quélet in 1884, in the form of  Psalliota bitorquis (using another genus name in place of the modern "Agaricus"). Description. The cap is dry, smooth, and white (but stains yellowish in age), and measures 4 to 15 cm in diameter, convex to flat, often with dirt on the cap. The gills are free, very narrow and close. They are a light pink color when young, becoming dark reddish-brown as the spores mature. The spore print is chocolate brown. The stipe is 3–11 cm long, 1–4 cm thick, cylindrical to clavate (club-shaped), stout, white, smooth, with a membranous veil and thick white mycelial sheathing near the  base. Distinctively it has both a thick upper ring which is shaped like a funnel and a thinner skirt-like lower ring, giving rise to the species name "bitorquis". The flesh is solid and firm, with a mild odor. It is often confused with the briny-smelling "Agaricus bernardii". It also resembles "Agaricus campestris" somewhat, but that species only has a single fragile ring. Microscopic details. Basidiospores are elliptical in shape, smooth, and with dimensions of 5–7 x 4–5.5 µm. Basidia are 20–25 x 6.5–8.5 µm, usually four-spored, but often with two-spored basidia present. Cystidia are present and  numerous. Distribution and habitat. "Agaricus bitorquis" may be found growing solitary or in small groups in gardens (noted as growing in a gregarious manner), and at roadsides, usually on the pavement, often where salt is applied to combat ice in winter. Pushing through asphalt and slabs, it is subterranean, and often matures underground. It is occasional throughout North America, Europe, Asia and Australia. Edibility. "Agaricus bitorquis" is a choice edible species, with a typical 'mushroomy' taste. Specimens collected in the wild may be gritty due to its often subterranean habitat. As with all specimens picked from the wild, care should  be taken to consider the suitability of the collection site, as this species can bioaccumulate toxic heavy metals, especially lead, from polluted areas. Nutritional analysis has shown this species to contain 18 amino acids, including all of the essential ones. Cultivation. First cultivated commercially in 1968, "A. bitorquis" has several growth characteristics that have piqued the interest of mushroom cultivators looking for an alternative to the standard button mushroom, "A. bisporus". For example, "A. bitorquis" is more resistant to various viral diseases, can grow at higher temperatures and CO concentrations, and has better resistance to bruising. Furthermore, high temperature-resistant  strains have recently been developed which may help cultivators overcome problems associated with cooling production rooms during hot summer months.