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BIODIVERSITY REFERENCE
 
   Agrocybe rivulosa Nauta   


Kingdom: Fungi
Phylum: Basidiomycota
Class: Agaricomycetes
Order: Agaricales

British distribution: An evident introduction, now frequent north to at least the south of Scotland.
World distribution: Western Europe, an evident introduction; native origin unknown.


Agrocybe rivulosa
Agrocybe rivulosa
Agrocybe rivulosa
Agrocybe rivulosa
Agrocybe rivulosa, abundant on heap of wood-chips, Muirshiel Country Park, Renfrewshire, October 2006.

 
A. rivulosa is a toadstool that has recently made spectacular appearance in Britain on wood-chips, generally where these are stored in heaps but also on paths. It was first named as a species in 2003, based on a find at Rotterdam in the Netherlands in 1999 (Nauta 2002, 2003, cited in de Haan, 2003), and is said to have been first found in Britain in 2004, though there is an apparent record in the FRDBI from the 1990s. In 2006 it appeared in numerous localities throughout much of the country, including the occurrence of some hundreds of fruitbodies at Muirshiel Country Park, documented here. It has since become a fairly well known species and is also spreading elsewhere in western Europe. Undoubtedly it is an introduction, but its origin is unknown.


Identification
A. rivulosa is a relatively large species, to 15cm in height and cap 12cm in diameter, the cap pallid to ochre yellow or pale orange-brown. The cap initially is rounded-conical, becoming expanded, somewhat moist, with conspicuous radial wrinkles. The stem is white, with a large, hanging, white, rather fragile, membranous ring. The gills are pale grey, becoming grey-brown. The spores are dull brown, as in other Agrocybe species. There is no volva.

Another Agrocybe that has recently appeared in Britain on wood-chips is A. putaminum. First recorded at Kew in 1986, it appeared in Manchester in 1996 and now appears to be increasing in southern England. It differs from A. rivulosa in lacking a ring, and the cap is described as having the texture of chamois leather. Both species are included in Buczacki et al. (2012), though the illustration purporting to be A. rivulosa seems more likely to represent A. putaminum.

Correct identification becomes essential if A. rivulosa is eaten. We have no folk lore history of experience of this species, no information on whether people may react to it in different ways, yet several websites claim it is edible — though there are French websites that state, "sa comestibilité est sans intérêt." The possible trap I have not seen mentioned is the potential for confusion with dangerously and fatally poisonous Amanita species. Some of the first Internet photographs of A. rivulosa were first identified as Death Cap (Amanita phalloides) and confusion could happen in the opposite direction! My experience with Internet identification forums is that people with very little knowledge can make completely confident but utterly ridiculous identifications — indeed "identification" apparently consists of finding a superficially similar Internet photograph, without any understanding of key characters and not reading any accompanying text. Volval characters in Amanita are variable and I have had one person belligerently adamant that his photograph was not an Amanita, and had no ring or volva, when remains of both were clearly visible in the photograph. In A. phalloides, the volva is fragile and can soon fall apart.

Now, Dear Reader, obviously you, yourself, are more intelligent than this, but imagine A. rivulosa is being collected along a wood-chip path. It has been carefully checked, including the brown spore-print, but overlooked has been one fruitbody that was actually a brownish variant of the Death Cap, or maybe a discoloured Destroying Angel (Amanita virosa), that has pushed up through the wood-chips from soil and tree roots below. It only takes that one fruitbody to turn a meal into a tragedy.

 

References
•   Buczacki, S., Shields, C., & Ovenden, D. (2012). Collins fungi guide, HarperCollins, London.
•   Haan, A. de, (2003) De geaderde leemhoed (Agrocybe rivulosa), een immigrant uit het noorden. Antwerpensen Koepel voor Naturstudie, Jaarboek 2003, http://www.provincieantwerpen.be/binaries/Ankonajaarboek_2003_De%20geaderde%20leemhoed%20%28Agrocybe%20rivulosa%29_tcm7-87485.pdf [accessed online, 18.05.2014]



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