Inocybe rimosa

What You Should Know

Inocybe rimosa (formerly known as Inocybe fastigiata) is a poisonous mushroom native to Europe. Its toxic ingredient is muscarine, discovered during the 1930s. Serious poisoning can result from consuming any quantity of the mushroom. It has a brownish fibrous cap, and stalk that lacks a ring.

Inocybe is a difficult genus, with numerous 'little brown mushrooms (LBMs as they are commonly called) that to the naked eye appear to be identical until they are examined under a microscope.

In Israel, it is confused with edible mushrooms of the genus Tricholoma, particularly Suillus granulatus, all of which grow in similar habitats.

Other names: Straw-Colored Fibre-Head, Split Fibrecap, Deadly Inocybe.

Inocybe rimosa Mushroom Identification

1. Ecology

   Mycorrhizal with hardwoods or conifers; growing alone, scattered, or gregariously; summer and fall (and winter in California); widely distributed in North America.

2. Cap

   2-8 cm; conical to bell-shaped, becoming broadly bell-shaped, usually with a sharp and distinct central bump; dry; silky or finely hairy; straw yellow to yellowish or yellowish-brown; the margin splitting and the surface becoming radially separated.

3. Gills

   Attached to the stem but sometimes pulling away from it in age; close or crowded; whitish, becoming grayish and then brownish with maturity (sometimes developing a greenish cast).

4. Stem

   3-9 cm long; up to 1 cm thick; more or less equal, without a swollen base; dry; smooth or finely silky; sometimes twisted or grooved; whitish or pale yellowish.

5. Flesh

   Whitish; insubstantial.

6. Odor

   Spermatic, mealy, or lacking.

7. Spore Print

   Brown.

8. Microscopic Features

   Spores 9.5-14.5 x 6-8.5 µ; elliptical; smooth. Pleurocystidia absent. Cheilocystidia 30-65 x 10-22; cylindrical to nearly clavate; thin-walled.

Inocybe rimosa Look-Alikes

1. Inocybe geophylla

   The white variety is smaller and paler.

2. Inocybe erubescens (synonym Inocybe patouillardii)

   Initially pale cream rather than straw yellow and it gradually becomes brick red; it is deadly poisonous.

Inocybe rimosa Taxonomy and Etymology

In 1789 French naturalist Jean Baptiste Francois (Pierre) Bulliard described this mushroom scientifically, giving it the name Agaricus rimosus. It was German mycologist Paul Kummer who, in 1871, transferred this species to the genus Inocybe, whereupon it acquired its currently-accepted scientific name Inocybe rimosa.

This little mushroom has numerous synonyms including Agaricus fastigiatus Schaeff., Agaricus rimosus Bull., Gymnopus rimosus (Bull.) Gray, Inocybe rimosa var. rimosa (Bull. P. Kumm., Inocybe fastigiata (Schaeff.) Quél.,

Inocybe, the genus name, means 'fibrous head', while the specific epithet rimosa is derived from the Latin adjective rimosus meaning 'full of cracks or fissures'.

Sources:

Photo 1 - Author: Ron Pastorino (Ronpast) (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 2 - Author: Jerzy Opioła (Creative Commons Attribution-Share Alike 4.0 International)

Photo 3 - Author: Eric Steinert (Creative Commons Attribution-Share Alike 2.5 Generic, 2.0 Generic and 1.0 Generic)

Photo 4 - Author: Dick Culbert from Gibsons, B.C., Canada (Creative Commons Attribution 2.0 Generic)