Clitocybe rivulosa (Sowerby) P. Kumm. - Fool's Funnel

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

Clitocybe rivulosa

The distinction between Clitocybe rivulosa and Clitocybe dealbata is generally considered to be dubious, because both macroscopically and microscopically the differences in physical characters, if evident at all, are minimal. Most authorities treat these two species as synonymous, while some still differentiate between them mainly on habitat: Clitocybe dealbata being found in humus-rich grassland and Clitocybe rivulosa occuring in sandy grassland, particularly coastal dune systems.

We are treating Clitocybe rivulosa and Clitocybe dealbata as one and the same species. These poisonous mushrooms often grow in fairy rings, and so anyone gathering Fairy Ring Champignons, Marasmius oreades, and St George's Mushrooms, Calocybe gambosa, or any other pale edible mushrooms that produce fairy rings must be very careful to ensure that they identify every single specimen with complete certainty.

Clitocybe rivulosa in grassland

Distribution

Taken together (because that's all we can hope to do in the field) Clitocybe rivulosa/Clitocybe dealbata are fairly common and widespread throughout much of Britain and Ireland. These toxic toadstools are found also in most parts of mainland Europe and in North America.

These very poisonous fungi contain the toxin muscarine, and so great care is essential if gathering any white-gilled mushrooms (for example Calocybe gambosa, St George's Mushroom) that are intended for consumption.

Taxonomic history

This species was described in 1801 by Christiaan Hendrik Persoon, who gave it the binomial scientific name Agaricus rivulosus. (At that time most gilled fungi were initially placed in a gigantic Agaricus genus, which has since been slimmed down with most of its contents being transferred to other newer genera.) In 1871 German mycologist Paul Kummer transferred this species to the genus Clitocybe, establishing its currently-accepted scientific name as Clitocybe rivulosa.

Synonyms of Clitocybe rivulosa include Agaricus rivulosus Pers., Agaricus rivulosus var. neptuneus Berk. & Broome, Clitocybe dealbata var. minor Cooke, Clitocybe rivulosa var. neptunea (Berk. & Broome) Massee, and Clitocybe dealbata - the latter no longer being recognised as a separate species.

Etymology

The generic name Clitocybe means 'sloping head', while the specific epithet rivulosa comes from the Latin word for a channel, river, or stream and in this instance is perhaps a reference to the faint channels or annular ridges that tend to form on mature caps of this mushroom.

Toxicity

Clitocybe rivulosa is a deadly poisonous and fairly common species that grows in habitats where people expect to find edible mushrooms. That makes it very dangerous indeed. The symptoms of poisoning by this and several similar whited-capped Clitocybe species are those associated with muscarine poisoning. Excessive salivation and sweating set in within half an hour of eating these fungi. Depending on the amount consumed, victims may also suffer abdominal pains, sickness and diarrhea, together with blurred vision and laboured breathing. Deaths of otherwise healthy people from eating these fungi are very rare, but anyone with a weakened heart or with respiratory problems is much more at risk.

Identification guide

Cap of Clitocybe rivulosa

Cap

1 to 6cm across; convex, flattening often with a wavy margin that is usually inrolled, sometimes developing a shallow central depression or becoming shallowly funnel shaped; smooth and floury or silky when dry; white, usually developing a slight buffish tinge with age.

With age faint concentric rings often become apparent on the cap surface, which in very dry weather tends to crack.

Gills of Clitocybe rivulosa

Gills

Adnate or slightly decurrent; crowded; white, developing a greyish pink tinge with age.

Stem of Clitocybe rivulosa

Stem

3 to 4cm long and 0.4 to 1cm in diameter; smooth and floury or silky; white; downy at the base; no stem ring.

Spores of Clitocybe rivulosa

Spores

Ellipsoidal, smooth, 4-5.5 x 2-4.5μm.

Spore print

White.

Odour/taste

Odour sweet but not distinctive; tasting this toxic toadstool is not recommended.

Habitat & Ecological role

In unimproved grassland, particularly on roadside verges and in parkland; also in coastal sand dune systems.

Season

July to early December in Britain and Ireland.

Similar species

Calocybe gambosa, St George's Mushroom, has thicker cap flesh and a mealy odour; it occurs in similar habitats but mainly between late April and early July.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

British Mycological Society (2010). English Names for Fungi

Funga Nordica, Henning Knudsen and Jan Vesterholt, 2008.

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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