Agrocybe rivulosa Nauta - Wrinkled Fieldcap

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

Agrocybe rivulosa, mature specimen

Unknown until 2003 and added to the British list in 2004, this fieldcap has since become fairly common in southern England, where its spread has been entirely due to the practice of mulching flowerbeds using wood chippings. (If it is ever given a common name, that might well have to be the 'Woodchip Fieldcap'.)

Agrocybe rivulosa

Many other fieldcaps are found on woodchip mulch, but the wrinkled cap of this mushroom is a great aid to its identification.

Distribution

An increasingly frequent find in southern England and in Ireland but also recorded occasionally in Wales and Scotland, where it is most often seen on heaps or on deep layers of woodchip, the Wrinkled Fieldcap occurs also in parts of mainland Europe, notably in Holland where it was first recorded.

Taxonomic history

This species was first recorded and described in 2003 as Agrocybe rivulosa by Dutch mycologist Marijke M. Nauta and published in Persoonia; it does not (yet!) have any synonyms.

Note: In some field guides this mushroom is recorded in the family Bolbitiaceae.

Etymology

Agrocybe rivulosa and a minority of other fieldcap fungi do not occur in open fields; nevertheless, the generic name Agrocybe is derived from Agro-, of fields, and -cybe, head or cap. The specific epithet rivulosa is a reference to the wrinkled grooves that descend like rivulets from the centre of the caps.

Identification guide

Cap of Agrocybe rivulosa

Cap

4 to10cm across, hemispherical becoming broadly convex or flat; the pale ochraceous surface develops radial wrinkles linked by a network of cross-veins - hence the common name Wrinkled Fieldcap.

Gills of Agrocybe rivulosa

Gills

Adnate; initially creamy-grey, turning grey-brown as spores mature.

Stem

5 to 10cm long and 1 to 1.5cm dia.; hollow; tapering slightly towards the apex; white, turning a pale creamy-ochre with age; persistent, thin pendulous stem ring.

Spores

Ellipsoidal, smooth, 11.5-12 x 7-8µm; with a distinct germ pore.

Spore print

Brown.

Show larger image

Odour/taste

Not distinctive

Habitat & Ecological role

Saprobic, on large groups or tufts on woodchip piles and on deeply-mulched flowerbeds.

Season

June to October in Britain and Ireland.  

Similar species

Agrocybe praecox, which occurs in spring and early summer, often grows in woodchip mulch; it is typically smaller and usually has a darker cap.

Culinary Notes

The Wrinkled Fieldcap Agrocybe rivulosa is still fairly rare and it is not generally reported to be edible, although there is at least one report of it being eaten with no discernible adverse effects. (A close relative, the Poplar Fieldcap Agrocybe cylindracea, is considered a good edible mushroom.) We cannot conform that this mushroom is safe and good to eat in the long term or that it does not upset some people's stomachs, and so do not recommend gathering and eating it.

Agrocybe rivulosa, showing mycelium at base

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

Nauta, M.M. 2003. A new Agrocybe on woodchips in northwestern Europe. Persoonia 18(2): 270-274

BMS List of English Names for Fungi

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.

Acknowledgements

Several of the pictures on this page were kindly provided by Simon Harding.

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