Clitocybe rivulosa

What You Should Know

These poisonous mushrooms often grow in fairy rings, and so anyone gathering Fairy Ring Champignons, 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.

There is some controversy as to whether Clitocybe dealbata and Clitocybe rivulosa (the Fool’s Funnel) are close variants of the same species or separate species, with dealbata growing inland and rivulosa growing nearer the coast. The gills are important for separating these two mushrooms. The gills of the Fairy Ring Champignon gills are free of the stem while the gills of the Ivory Funnel are decurrent, they run down the stem.

Clitocybe rivulosa Mushroom Identification

1. Pileus

   Cap 2.0-4.0 cm broad, shallowly convex in youth, expanding to nearly plane with a slightly depressed to umbonate disc; margin incurved, then decurved to occasionally raised in age; surface canescent, white, ashy-gray to grayish-tan; streaked or water-spotted at maturity; context thin, 3.0-4.0 mm thick at the disc, 1-2 mm at the margin; context soft, cream-buff, unchanging; odor mild; taste mild to slightly astringent with time.

2. Lamellae

   Gills adnate at first, subdecurrent in age, close, cream-buff, becoming tan, relatively narrow; lamellulae in three to four series.

3. Stipe

   Stipe 2.0-4.0 cm long, 4.0-8.0 mm thick, equal to enlarged at the apex, straight or curved, solid in youth, eventually hollow, often flattened in cross section, not leathery or tough; surface appressed fibrillose, pallid, darkening where handled; partial veil absent.

4. Spores

   Spores 4.0-5.0 x 2.0-3.0 µm, smooth, thin-walled, elliptical-oblong in face-view, elliptical and inequilateral in profile, hilar appendage well-developed, inamyloid; spores white in deposit.

5. Habitat

   In arcs and rings in grasslands and pastures; fruiting from late fall to mid-winter; infrequent to occasionally common.

6. Spore print: White.

Clitocybe rivulosa Taxonomy and Etymology

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.

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.

Clitocybe rivulosa 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.

Sources:

Photo 1 - Author: Strobilomyces (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 2 - Author: Andreas Kunze (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 3 - Author: Георгий Виноградов (Georgy Vinogradov) (Creative Commons Attribution 4.0 International)

Photo 4 - Author: gailhampshire from Cradley, Malvern, U.K (Creative Commons Attribution 2.0 Generic)