Agaricus bitorquis (Quél.) Sacc. - Pavement Mushroom

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Agaricales - Family: Agaricaceae

Agaricus bitorquis - Pavement Mushroom, West Wales

Agaricus bitorquis, commonly known as the Pavement Mushroom because it often appears on the edges of pavements and sometimes even erupts through asphalt or pushes open the gaps between paving slabs, is an edible mushroom.

Distribution

Pavement Mushrooms are uncommon to rare in most parts of Britain and Ireland, but where they do occur these mushrooms are more often seen in small groups rather than as singletons.

Agaricus bitorquis - Pavement Mushroom

Agaricus bitorquis occurs also on mainland Europe and in parts of North America.

Taxonomic history

The specific name bitorquis was given to this mushroom by Lucien Quélet - often written as Quelet without the accent - in 1883 (published 1884), who called it Psalliota bitorquis. Italian mycologist Pier Andrea Saccardo (1845 - 1920) moved the Pavement Mushroom to its present genus Agaricus in 1887.

Synonyms of Agaricus bitorquis include Chitonia pecquinii Boud., Agaricus campestris var. edulis Vittad., Agaricus rodmanii Peck, Psalliota bitorquis Quél., Psalliota peronata Richon & Roze, Psalliota rodmanii (Peck) Kauffman, Psalliota edulis (Vittad.) Jul. Schäff. & F.H. Møller, Psalliota edulis var. valida F.H. Møller, and Agaricus bitorquis var. validus (F.H. Møller) Bon & Cappelli.

Etymology

The Latin word bitorquis means 'with two collars' - a reference to the double ring that results when the partial veil covering the young gills tears from the cap rim, leaving thin white annuli where the veil was attached at two regions of the stem, one high up and the other lower down.

Identification guide

Cap of Agaricus bitorquis

Cap

Initially convex and then becoming flattened, the surface of the cap of Agaricus bitorquis is white and finely flaky or scaly; the thick cap flesh is white, turning slightly pink on exposure to air. More often than not the cap surface is discoloured by earth, and in some instances these mushroom actually mature underground or with only a small part of the cap rim visible from above ground.

At maturity, the cap diameter is between  5 and 10cm.

Gills and stem of Agaricus bitorquis

Gills

The free gills are narrow and densely spaced; pale pink when young, becoming, reddish-brown as the spores mature.

Stem

Cylindrical or narrowing slightly towards the apex and towards the slightly rooting base, stems are usually 4-6cm long and 2-4cm in diameter; a membranous double ring persists.

Spores of Agaricus bitorquis

Basidia

Mostly four-spored but some two-spored basidia may also be found.

Spores

Subglobose, 5-7 x 4-5.5µm.

Spore print

Deep chocolate brown.

Odour/taste

Not distinctive.

Habitat & Ecological role

Saprobic, on dry soil beside footpaths; occasionally it is to be seen pushing up through tarmac or in the gaps between paving slabs.

Season

Late spring to autumn.

Similar species

Agaricus bernardii is similar but can be distinguished from the Pavement Mushroom by its salty odour and the fact that its flesh reddens when cut.

Agaricus campestris, the Field Mushroom, is somewhat similar in appearance but has a more substantial single ring; it is usually taller for the same cap diameter.

Agaricus bitorquis - Pavement Mushroom, roadside verge

Culinary Notes

There is nothing about the appearance or location of these often worm-ridden fungi that cries out 'eat me', and although often reported to be edible they are surely best left to drop their spores and then rot away.

Reference Sources

Pat O'Reilly (2016) Fascinated by Fungi; First Nature

BMS List of English Names for Fungi

The genus Agaricus in Britain, 3rd Edition, self-published, Geoffrey Kibby 2011

Funga Nordica: 2nd edition 2012. Edited by Knudsen, H. & Vesterholt, J. ISBN 9788798396130

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

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