Agrocybe rivulosa on woodchip, Melincwrt
Agrocybe rivulosa was first discovered in Holland in 2003. By 2004, it was found in Britain and has since spread throughout the country, growing exclusively (as far as I am aware) on wood-chip or mulch. This large troop of specimens was found this weekend on a wood-chip pile in Melincwrt, near Resolven. This is the first time I've seen it in Neath Port Talbot.
Because it is a new addition to the fungus 'flora' of Britain, it isn't described or illustrated in many books. For example, it isn't included in the revised edition of Roger Phillip's Mushrooms. However there are several good photos on line and one in the Collins Complete Guide to British Mushrooms & Toadstools (Paul Sterry and Barry Hughes, 2009). There is also an illustration in the Collins Fungi Guide (Stefan Buczacki, Chris Shields and Denys Ovenden, 2012), but that doesn't show the most distinctive features of this species. The young, expanding fruiting bodies have a distinctive ring on their stems and a pale, wrinkled cap. The wrinkled-skin like appearance of the cap cuticle is very noticeable, as shown in the photo below. The gills are pale at first, then turn a dark grey-brown due to spore production.
Young specimens of Agrocybe rivulosa
Older specimens seem to develop a darker cap colour (see top photo), especially when wet, but this feature is rarely mentioned in guide books.